Bethel College Review Of Forensic Science Paper

Part I

***The minimum word count for the entire is 250 words and you must include three scholarly sources! Scholarly sources does not count toward word count! You must use APA formatting to cite your sources. Be sure to read the entire assignment and address each issue/question posed. (References doesn’t count towards word count!)***

Q1.
Police discover a badly decomposed body buried in an area where a man disappeared some years ago. The case was never solved, nor was the victim’s body ever recovered. As the lead investigator, you suspect the body is that of the missing victim. What is your main challenge in using DNA to determine whether it is or is not? How would you go about using DNA technology to test your theory?

Part II

***The minimum word count for the entire is 1300 words and you must include three scholarly sources! Scholarly sources does not count toward word count! You must use APA formatting to cite your sources. Be sure to read the entire assignment and address each issue/question posed. (References doesn’t count towards word count)***

Case Study: Use the Internet and Chapter 15 of your text to research convicted murderer Timothy McVeigh.

1. Case Summary

In a narrative format, discuss the key facts and critical issues presented in the case.

2. Case Analysis

Give a detailed summary of the forensic investigation’s findings along with the evidence against Mr. McVeigh.

3.
Executive Decisions

As lead investigator, prepare a summary for the prosecutor that explains the types of explosives used and their design and detonation.

chapter
15
DNA: the indispensable
forensic science tool
Learning Objectives
M
I
L
E
S
,
S
After studying this chapter you should be able to:
H
t
Name the parts of a nucleotide and explain how they are
A
linked together to form DNA
N
t
Understand the concept of base pairing as it relates to the
N
double-helix structure of DNA
O
t
Contrast DNA strands that code for the production
of proteins
with strands that contain repeating base sequences
N
t
Explain the technology of polymerase chain reaction (PCR)
and how it applies to forensic DNA typing1
t
Understand the concept of electrophoresis9
0
9 mitochondrial
t
Describe the difference between nuclear and
DNA
T
t
Understand the use of DNA computerizedSdatabases in
t
Understand the structure of an STR
criminal investigation
ISBN: 978-1-323-16745-8
t
List the necessary procedures for the proper preservation
of bloodstained evidence for laboratory DNA analysis
KEY TERMS
amelogenin gene
amino acids
buccal cells
chromosome
complementary base
pairing
deoxyribonucleic acid
(DNA)
electrophoresis
epithelial cells
human genome
hybridization
low copy number
mitochondria
multiplexing
nucleotide
picogram
polymer
polymerase chain
reaction (PCR)
primer
proteins
replication
restriction fragment
length polymorphisms (RFLPs)
sequencing
short tandem repeat
(STR)
substrate control
tandem repeat
touch DNA
Y-STRs
Criminalistics: An Introduction to Forensic Science, Eleventh Edition, by Richard Saferstein. Published by Prentice Hall. Copyright © 2015 by Pearson Education, Inc.
378
CHAPTER 15
deoxyribonucleic acid (DNA)
The molecules carrying the body’s
genetic information; DNA is
double stranded in the shape of a
double helix.
chromosome
A rodlike structure in the cell
nucleus, along which the genes are
located; it is composed of DNA
surrounded by other material,
mainly proteins.
polymer
A substance composed of a large
number of atoms; these atoms are
usually arranged in repeating units,
or monomers.
nucleotide
The unit of DNA consisting of one
of four bases—adenine, guanine,
cytosine, or thymine—attached to
a phosphate–sugar group.
The discovery of deoxyribonucleic acid (DNA), the deciphering of its structure, and the decoding of its genetic information were turning points in our understanding of the underlying concepts
of inheritance. Now, with incredible speed, as molecular biologists unravel the basic structure of
genes, we can create new products through genetic engineering and develop diagnostic tools and
treatments for genetic disorders.
For a number of years, these developments were of seemingly peripheral interest to forensic
scientists. All that changed when, in 1985, what started out as a more or less routine investigation into the structure of a human gene led to the discovery that portions of the DNA structure
of certain genes are as unique to each individual as fingerprints. Alec Jeffreys and his colleagues
at Leicester University, England, who were responsible for these revelations, named the process
for isolating and reading these DNA markers DNA fingerprinting. As researchers uncovered new
approaches and variations to the original Jeffreys technique, the terms DNA profiling and DNA
typing came to be applied to describe this relatively new technology.
This discovery caught the imagination of the forensic science community because forensic
scientists have long desired to link with certainty biological evidence such as blood, semen, hair,
M
or tissue to a single individual. Although conventional testing procedures had gone a long way
toward narrowing the source ofIbiological materials, individualization remained an elusive goal.
Now DNA typing has allowed forensic scientists to accomplish this goal. The technique is still
L
relatively new, but in the few years since its introduction, DNA typing has become routine in
public crime laboratories and has
E been made available to interested parties through the services
of a number of skilled private laboratories. In the United States, courts have overwhelmingly
S
admitted DNA evidence and accepted the reliability of its scientific underpinnings.
,
A
What Is DNA? S
S
P
G
S
P
T
S
P
Inside each of 60 trillion cells in the human body are strands of genetic material called
H
chromosomes. Arranged along the chromosomes, like beads on a thread, are nearly 25,000
A unit of heredity. It instructs the body cells to make proteins
genes. The gene is the fundamental
that determine everything from N
hair color to our susceptibility to diseases. Each gene is actually
composed of DNA specifically designed to carry out a single body function.
Nwas first discovered in 1868, scientists were slow to understand
Interestingly, although DNA
and appreciate its fundamental role
O in inheritance. Painstakingly, researchers developed evidence
that DNA was probably the substance by which genetic instructions are passed from one generation to the next. But the major N
breakthrough in comprehending how DNA works did not occur
until the early 1950s, when two researchers, James Watson and Francis Crick, deduced the structure of DNA. It turns out that DNA is an extraordinary molecule skillfully designed to carry out
1 traits of all living cells, plant and animal.
the task of controlling the genetic
9
0 of Watson and Crick’s discovery, let’s see how DNA is conBefore examining the implications
structed. DNA is a polymer. As9we will learn in Chapter 12, a polymer is a very large molecule
made by linking a series of repeating units.
T
NUCLEOTIDES In the case of DNA, the repeating units are known as nucleotides. A nucleotide
S a phosphorus-containing group, and a nitrogen-containing
is composed of a sugar molecule,
Structure of DNA
C
S
P
molecule called a base. Figure 15–1 shows how nucleotides can be strung together to form a
DNA strand. In this figure, S designates the sugar component, which is joined with a phosphate
group to form the backbone of the DNA strand. Projecting from the backbone are the bases.
The key to understanding how DNA works is to appreciate the fact that only four types of
bases are associated with DNA: adenine, cytosine, guanine, and thymine. To simplify our discussion of DNA, we will designate each of these bases by the first letter of their names. Hence,
A will stand for adenine, C will stand for cytosine, G will stand for guanine, and T will represent
thymine.
Again, notice in Figure 15–1 how the bases project from the backbone of DNA. Also, although this figure shows a DNA strand of four bases, keep in mind that in theory there is no
limit to the length of the DNA strand; in fact, a DNA strand can be composed of a long chain
with millions of bases. The information just discussed was well known to Watson and Crick by
Criminalistics: An Introduction to Forensic Science, Eleventh Edition, by Richard Saferstein. Published by Prentice Hall. Copyright © 2015 by Pearson Education, Inc.
ISBN: 978-1-323-16745-8
FIGURE 15–1
How nucleotides can be
linked to form a DNA
strand. S designates
the sugar component,
which is joined with
phosphate groups (P) to
form the backbone of
DNA. Projecting from
the backbone are four
bases: A, adenine; G,
guanine; T, thymine;
and C, cytosine.
DNA: THE INDISPENSABLE FORENSIC SCIENCE TOOL
379
the time they set about detailing the structure of DNA. Their efforts led to the discovery that the
DNA molecule is actually composed of two DNA strands coiled into a double helix. This can be
thought of as resembling two wires twisted around each other.
As these researchers manipulated scale models of DNA strands, they realized that the
only way the bases on each strand could be properly aligned with each other in a double-helix
configuration was to place base A opposite T and G opposite C. Watson and Crick had solved
the puzzle of the double helix and presented the world with a simple but elegant picture of DNA
(see Figure 15–2).
COMPLEMENTARY BASE PAIRING The only arrangement possible in the double-helix
configuration was the pairing of bases A to T and G to C, a concept that has become known as
complementary base pairing. Although A–T and G–C pairs are always required, there are no
restrictions on how the bases are to be sequenced on a DNA strand. Thus, one can observe the
sequences T–A–T–T or G–T–A–A or G–T–C–A. When these sequences are joined with their
complements in a double-helix configuration, they pair as follows:
T A T T
| |
| |
A T A A
complementary base pairing
The specific pairing of base A
with T and base G with C in
double-stranded DNA.
M
G T A A
| | | |
C A T T
G T C A
| I| | |
C L
A G T
Any base can follow another on a DNA strand, which means E
that the possible number of different sequence combinations is staggering! Consider that the average human chromosome has
S
DNA containing 100 million base pairs. All of the human chromosomes
taken together contain
about 3 billion base pairs. From these numbers, we can begin to appreciate
the diversity of DNA
,
S
H
A
N
N
O
N
G
A
S
P
C
S
G
P
S
T
C
T
A
1
9
0
9
S
T
P
SS
P
S
P
ISBN: 978-1-323-16745-8
P
S
G
C
S
FIGURE 15–2
A representation of a DNA double helix. Notice how bases G and C pair with each
other, as do bases A and T. This is the only arrangement in which two DNA strands can
align with each other in a double-helix configuration.
Criminalistics: An Introduction to Forensic Science, Eleventh Edition, by Richard Saferstein. Published by Prentice Hall. Copyright © 2015 by Pearson Education, Inc.
380
CHAPTER 15
WEBEXTRA 15.1
and hence the diversity of living organisms. DNA is like a book of instructions. The alphabet
used to create the book is simple enough: A, T, G, and C. The order in which these letters are arranged defines the role and function of a DNA molecule.
What Is DNA?
DNA at Work
proteins
Polymers of amino acids that play
basic roles in the structures and
functions of living things.
amino acids
The building blocks of proteins;
there are twenty common amino
acids; amino acids are linked to
form a protein; the types of amino
acids and the order in which they’re
linked determine the character of
each protein.
Normal
hemoglobin
Sickle-cell
hemoglobin
1
valine
valine
2
histidine
histidine
3
leucine
leucine
4
threonine
threonine
5
proline
proline
6
glutamate
valine
7
glutamate
glutamate
(a)
(b)
FIGURE 15–3
(a) A string of amino acids
composes one of the protein chains of hemoglobin.
(b) Substitution of just one
amino acid for another in
the protein chain results in
sickle-cell hemoglobin.
The inheritable traits that are controlled by DNA arise out of its ability to direct the production
of complex molecules called proteins. Proteins are actually made by linking a combination of
amino acids. Although thousands of proteins exist, they can all be derived from a combination
of up to 20 known amino acids. The sequence of amino acids in a protein chain determines the
shape and function of the protein. Let’s look at one example: The protein hemoglobin is found
in our red blood cells. It carries oxygen to our body cells and removes carbon dioxide from these
cells. One of the four amino acid chains of “normal” hemoglobin is shown in Figure 15–3(a).
Studies of individuals with sickle-cell anemia show that this inheritable disorder arises from the
M
presence of “abnormal” hemoglobin in their red blood cells. An amino acid chain for “abnormal”
hemoglobin is shown in FigureI 15–3(b). Note that the sole difference between “normal” and
“abnormal” or sickle-cell hemoglobin arises from the substitution of one amino acid for another
L
in the protein chain.
The genetic information that
E determines the amino acid sequence for every protein manufactured in the human body is stored in DNA in a genetic code that relies on the sequence of
S
bases along the DNA strand. The alphabet of DNA is simple—A, T, G, and C—but the key to deciphering the genetic code is to ,know that each amino acid is coded by a sequence of three bases.
Thus, the amino acid alanine is coded by the combination C–G–T; the amino acid aspartate is
coded by the combination C–T–A; and the amino acid phenylalanine is coded by the combinaS we can now see how the amino acid sequence in a protein
tion A–A–A. With this code in hand,
chain is determined by the structure of DNA. Consider the DNA segment
H
A
The triplet code contained within
Nthis segment translates into
[C–G–T] – [C–T–A] – [A–A–T] – [C–G–T]
N aspartate phenylalanine alanine
alanine
or the protein chain
O
alanine Naspartate
phenylalanine
alanine
–C–G–T–C–T–A–A–A–A–C–G–T–
Interestingly, this code is not restricted to humans. Almost all living cells studied to date use the
1 of protein synthesis.1
same genetic code as the language
If we look at the difference9
between “normal” and sickle-cell hemoglobin (see Figure 15–3),
we see that the latter is formed by substituting one amino acid (valine) for another (gluta0 that codes for the production of normal hemoglobin, the letter
mate). Within the DNA segment
sequence is
9
–[C–C–T]–[G–A–G]–[G–A–G]–
Tproline glutamate glutamate
S carry the sequence
Individuals with sickle-cell disease
–[C–C–T]–[G–T–G]–[G–A–G]–
proline
valine glutamate
1
Instructions for assembling proteins are actually carried from DNA to another region of the cell by ribonucleic acid
(RNA). RNA is directly involved in the assembly of the protein using the genetic code it received from DNA.
Criminalistics: An Introduction to Forensic Science, Eleventh Edition, by Richard Saferstein. Published by Prentice Hall. Copyright © 2015 by Pearson Education, Inc.
ISBN: 978-1-323-16745-8
Thus, we see that a single base or letter change (T has been substituted for A in valine) is the underlying cause of sickle-cell anemia, demonstrating the delicate chemical balance between health
and disease in the human body.
As scientists unravel the base sequences of DNA, they obtain a greater appreciation for the
roles that proteins play in the chemistry of life. Already the genes responsible for hemophilia,
DNA: THE INDISPENSABLE FORENSIC SCIENCE TOOL
Duchenne muscular dystrophy, and Huntington’s disease have been located. Once scientists have
isolated a disease-causing gene, they can determine the protein that the gene has directed the cell
to manufacture. By studying these proteins—or the absence of them—scientists will be able to
devise a treatment for genetic disorders.
A 13-year project to determine the order of bases on all 23 pairs of human chromosomes
(also called the human genome) is now complete. Knowing where on a specific chromosome
DNA codes for the production of a particular protein is useful for diagnosing and treating genetic
diseases. This information is crucial for understanding the underlying causes of cancer. Also,
comparing the human genome with that of other organisms will help us understand the role and
implications of evolution.
Replication of DNA
Once the double-helix structure of DNA was discovered, how DNA
M duplicated itself before cell
division became apparent. The concept of base pairing in DNA suggests the analogy of positive
I helix has the same informaand negative photographic film. Each strand of DNA in the double
tion; one can make a positive print from a negative or a negative L
from a positive.
381
human genome
The total DNA content found
within the nucleus of a human cell;
it is composed of approximately
three billion base pairs of genetic
information.
replication
The synthesis of new DNA from
existing DNA.
polymerase chain reaction
(PCR)
A technique for replicating or
copying a portion of a DNA strand
outside a living cell; this technique
leads to millions of copies of the
DNA strand.
E
The synthesis of new DNA from existing DNA begins with the unwinding
of the DNA strands in
S
the double helix. Each strand is then exposed to a collection of free nucleotides. Letter by letter, the
,
double helix is re-created as the nucleotides are assembled in the proper order, as dictated by the
The Process of Replication
ISBN: 978-1-323-16745-8
principle of base pairing (A with T and G with C). The result is the emergence of two identical copies of DNA where before there was only one (see Figure 15–4). A cell can now pass on its genetic
S
identity when it divides.
Many enzymes and proteins are involved in unwinding the H
DNA strands, keeping the two
DNA strands apart, and assembling the new DNA strands. For example, DNA polymerases are
A
enzymes that assemble a new DNA strand in the proper base sequence determined by the origiNgrowing DNA double helices
nal, or parent, DNA strand. DNA polymerases also “proofread” the
for mismatched base pairs, which are replaced with correct bases.
N
Until recently, the phenomenon of DNA replication appeared to be of only acaO
demic interest to forensic scientists interested in DNA for identification.
However,
this changed when researchers perfected the technology of using DNA polymerases
N
to copy a DNA strand located outside a living cell. This laboratory technique is
known as polymerase chain reaction (PCR). Put simply, PCR is a technique
designed to copy or multiply DNA strands in a laboratory test tube.
1
In PCR, small quantities of DNA or broken pieces of DNA found in crime9 The copying
scene evidence can be copied with the aid of a DNA polymerase.
process is highly temperature dependent and can be accomplished
0 in an automated fashion using a DNA thermal cycler (see Figure 15–5). Each cycle of
the PCR technique results in a doubling of the DNA, as shown 9
in Figure 15–4.
Within a few hours, 30 cycles can multiply DNA a billionfold. T
Once DNA copies are
in hand, they can be analyzed by any of the methods of modern molecular biology. The abilS for forensic scientists to
ity to multiply small bits of DNA opens new and exciting avenues
explore. It means that sample size is no longer a limitation in characterizing DNA recovered
from crime-scene evidence.
Parent DNA
unravels
New double
helices formed
FIGURE 15–4
Replication of DNA. The
strands of the original DNA
molecule are separated,
and two new strands are
assembled.
DNA Typing with Short Tandem Repeats
Tandem Repeats
Geneticists have discovered that portions of the DNA molecule contain sequences of letters that
are repeated numerous times. In fact, more than 30 percent of the human genome is composed of
repeating segments of DNA. These repeating sequences, or tandem repeats, seem to act as filler
or spacers between the coding regions of DNA. Although these repeating segments do not seem
tandem repeat
A region of a chromosome that
contains multiple copies of a core
DNA sequence that are arranged
in a repeating fashion.
Criminalistics: An Introduction to Forensic Science, Eleventh Edition, by Richard Saferstein. Published by Prentice Hall. Copyright © 2015 by Pearson Education, Inc.
382
CHAPTER 15
inside the science
Polymerase Chain Reaction
The most important feature of PCR is the knowledge
that an enzyme called DNA polymerase can be directed to synthesize a specific region of DNA. In a
relatively straightforward manner, PCR can be used
to repeatedly duplicate or amplify a strand of DNA
millions of times. As an example, let’s consider a segment of DNA that we want to duplicate by PCR:
–G–T–C–T–C–A–G–C–T–T–C–C–A–G–
–C–A–G–A–G–T–C–G–A–A–G–G–T–C–
To perform PCR on this DNA segment, short sequences of DNA on each side of the region of interest
must be identified. In the example shown here, the
short sequences are designated by boldface letters in
the DNA segment. These short DNA segments must
be available in a pure form known as a primer if the
PCR technique is going to work.
The first step in PCR is to heat the DNA strands to
about 94°C. At this temperature, the double-stranded
DNA molecules separate completely:
–G–T–C–T–C–A–G–C–T–T–C–C–A–G–
The second step is to add the primers to the separated strands and allow the primers to combine, or
hybridize, with the strands by lowering the test-tube
temperature to about 60°C.
M
I
L
E
S
,
S
–G–T–C–T–C–A–G–C–T–T–C–C–A–G–
H
–C–A–G–A
C–C–A–G
A
–C–A–G–A–G–T–C–G–A–A–G–G–T–C–
N
N The third step is to add the DNA polymerase and
mixture of free nucleotides (A, C, G, T) to the sepaOarated
strands. When the test tube is heated to 72°C,
Nthe polymerase enzyme directs the rebuilding of a
double-stranded DNA molecule, extending the primers by adding the appropriate bases, one at a time,
1resulting in the production of two complete pairs of
double-stranded DNA segments:
9
0
9
T
S
–G–T–C–T–C–A–G–C–T–T–C–C–A–G–
C–A–G–A–G–T–C–G–A–A–G–G–T–C–
G–T–C–T–C–A–G–C–T–T–C–C–A–G
–C–A–G–A–G–T–C–G–A–A–G–G–T–C–
This completes the first cycle of the PCR technique,
which results in a doubling of the number of DNA molecules from one to two. The cycle of heating, cooling,
and strand rebuilding is then repeated, resulting in a further doubling of the DNA molecules. On completion of
the second cycle, four double-stranded DNA molecules
have been created from the original double-stranded
DNA sample. Typically, 28 to 32 cycles are carried out
to yield more than one billion copies of the original
DNA molecule. Each cycle takes less than two minutes.
Criminalistics: An Introduction to Forensic Science, Eleventh Edition, by Richard Saferstein. Published by Prentice Hall. Copyright © 2015 by Pearson Education, Inc.
ISBN: 978-1-323-16745-8
–C–A–G–A–G–T–C–G–A–A–G–G–T–C–
Copyright © 2012 Life Technologies Corporation. Used under permission
FIGURE 15–5
The DNA Thermal Cycler, an
instrument that automates the
rapid and precise temperature
changes required to copy a
DNA strand. Within a matter of
hours, DNA can be multiplied a
millionfold.
DNA: THE INDISPENSABLE FORENSIC SCIENCE TOOL
383
primer
G–C–T G–G–T G–C–T G–G–C C–T–C
Fifteen–base core
FIGURE 15–6
A DNA segment consisting of a series of repeating DNA units. In this illustration, the
15-base core can repeat itself hundreds of times. The entire DNA segment is typically
hundreds to thousands of bases long.
A short strand of DNA used
to target a region of DNA for
replication by PCR.
hybridization
The process of joining two complementary strands of DNA to form a
double-stranded molecule.
WEBEXTRA 15.2
Polymerase Chain Reaction
to affect our outward appearance or control any other basic genetic function, they are nevertheless
part of our genetic makeup, inherited from our parents in the manner illustrated by the Punnett
square (page 366). The origin and significance of these tandem repeats is a mystery, but to forensic
scientists they offer a means of distinguishing one individual from another through DNA typing.
Forensic scientists first began applying DNA technology toM
human identity in 1985. From
the beginning, attention has focused on the tandem repeats of theI genome. These repeats can be
visualized as a string of connected boxes with each box having the same core sequence of DNA
Lbut there is tremendous variabases (see Figure 15–6). All humans have the same type of repeats,
tion in the number of repeats that each of us has.
E
Up until the mid-1990s, the forensic community aimed its efforts at characterizing repeat
S
segments known as restriction fragment length polymorphisms (RFLPs). A number of different RFLPs were selected by the forensic science community, for performing DNA typing.
Typically a core sequence is 15 to 35 bases long and repeats itself up to one thousand times.
These repeats are cut out of the DNA double helix by a restriction enzyme that acts like a pair
of scissors. Once the DNA molecules have been cut up by the restriction
enzyme, the resulting
S
fragments were sorted out by separating the fragments by a technique known as electrophoresis.
H
RFLP DNA typing has the distinction of being the first scientifically accepted protocol in the
A its utility has been short
United States used for the forensic characterization of DNA. However,
lived. New technology incorporating PCR has supplanted RFLP. In its short history, perhaps
N
RFLP’s most startling impact related to the impeachment trial of President Bill Clinton. The
whole complexion of the investigation regarding the relationshipNof the president with a White
House intern, Monica Lewinsky, changed when it was revealed that Ms. Lewinsky possessed a
O
dress that she claimed was stained with the president’s semen. The FBI Laboratory was asked to
compare the DNA extracted from the dress stain with that of the N
president. An RFLP match was
obtained between the president’s DNA and the stain. The combined frequency of occurrence for
the seven DNA types found was nearly one in eight trillion, an undeniable link. The dress and a
1
copy of the FBI DNA report are shown in Figure 15–7.
Why couldn’t the PCR technology be applied to RFLP DNA9typing? Simply put, the RFLP
strands are too long, often containing thousands of bases. PCR is best used with DNA strands that
0 to this problem is to characare no longer than a couple of hundred bases. The obvious solution
terize DNA strands that are much shorter than RFLPs. Another 9
advantage in moving to shorter
DNA strands is that they would be expected to be more stable and less subject to degradation
T strands tend to break apart
brought about by adverse environmental conditions. The long RFLP
under adverse conditions not uncommon at crime scenes.
S
ISBN: 978-1-323-16745-8
Short Tandem Repeats (STRs)
Currently, short tandem repeat (STR) analysis has emerged as the most successful and widely
used DNA-profiling procedure. STRs are locations (loci) on the chromosome that contain short
sequence elements that repeat themselves within the DNA molecule. They serve as helpful markers for identification because they are found in great abundance throughout the human genome.
STRs normally consist of repeating sequences of three to seven bases; the entire strand of an
STR is also very short, less than 450 bases long. These strands are significantly shorter than those
encountered in other DNA typing procedures. This means that STRs are much less susceptible
to degradation and are often recovered from bodies or stains that have been subject to extreme
decomposition. Also, because of their shortness, STRs are an ideal candidate for multiplication
by PCR, thus overcoming the limited-sample-size problem often associated with crime-scene
restriction fragment length
polymorphisms (RFLPs)
Different fragment lengths of
base pairs that result from cutting
a DNA molecule with restriction
enzymes.
electrophoresis
A technique for separating molecules through their migration on
a support medium while under the
influence of an electrical potential.
WEBEXTRA 15.3
An Animated Demonstration of Gel
Electrophoresis
short tandem repeat (STR)
A region of a DNA molecule that
contains short segments consisting
of three to seven repeating base
pairs.
Criminalistics: An Introduction to Forensic Science, Eleventh Edition, by Richard Saferstein. Published by Prentice Hall. Copyright © 2015 by Pearson Education, Inc.
1
9
0
9
FIGURE 15–7
The dress and the FBI Report of Examination for a semen stain
T located
on the dress.
S
Q3243
Courtesy of Federal Bureau of Investigation
S
H
A
N
N
O
N
Courtesy of Federal Bureau of Investigation
M
I
L
E
S
,
Criminalistics: An Introduction to Forensic Science, Eleventh Edition, by Richard Saferstein. Published by Prentice Hall. Copyright © 2015 by Pearson Education, Inc.
ISBN: 978-1-323-16745-8
384
inside the science
Electrophoresis
Electrophoresis is somewhat related to thin-layer
chromatography (discussed in Chapter 9) in that it
separates materials according to their migration rates
on a stationary solid phase. However, electrophoresis
does not use a moving liquid phase to move the material; instead, an electrical potential is placed across
the stationary medium.
The nature of the medium can vary; most forensic
applications call for a starch or agar gel coated onto a
glass plate. Under these conditions, only substances
that possess an electrical charge migrate across the
stationary phase (see Figure 1 [a–c]). Because many
substances in blood carry an electrical charge, they
Power source
Mixtures of DNA fragments
of different sizes placed on
gel-coated plate
Gel-coated plate
(a)
Power source
can be separated and identified by electrophoresis.
The technique is particularly useful for separating and
identifying complex biochemical mixtures. In forensic
science, electrophoresis is most useful for characterizing proteins and DNA in dried blood.
Forensic serologists have developed several electrophoretic procedures for characterizing DNA in dried
blood. Mixtures of DNA fragments can be separated
by gel electrophoresis by taking advantage of the fact
that the rate of movement of DNA across a gel-coated
plate depends on the molecule’s size. Smaller DNA
fragments move faster along the plate than larger
fragments. After completing the electrophoresis
M DNA
run, the separated DNA is stained with a suitable deI veloping agent for visual observation (see Figure 2).
L
E
S
,
Power source
Electric potential
applied to plate
S
(b)H
A
Separated bands allow analyst
N
to characterize DNA in dried blood
N
O
N
Substances with an
electrical charge
migrate across plate
Longer fragments
move more slowly
Shorter fragments
move more quickly
Completed gel
1
9
FIGURE 1
The technique of gel electrophoresis. (a) Applying samples
0 to the plate. (b) Applying electric potential to
the plate to cause the fragments to migrate. (c) Separation of the fragments on the gel allows for analysis.
9
FIGURE 2
T
DNA fragments separated
S
by gel electrophoresis are
(c)
Explorer/Science Source
ISBN: 978-1-323-16745-8
visualized under a UV light.
385
Criminalistics: An Introduction to Forensic Science, Eleventh Edition, by Richard Saferstein. Published by Prentice Hall. Copyright © 2015 by Pearson Education, Inc.
386
CHAPTER 15
A A
T
–
G
A
AA
T G
T G
T G
A A
T
G
AT
– A
T G
Dorling Kindersley Limited
A
AA
T G
G
A
–
A
–
T G
AA
–
–
AA
T G –
A
G
AT
– A
A
–
T G
–
T G
AA
–
–
M
I
L–
A A T G
AA
E
FIGURE 15–8
S
Variants of the short tandem repeat TH01. The upper DNA strand contains six
,
repeats of the sequence A-A-T-G;
the lower DNA strand contains eight repeats of the
sequence A-A-T-G. This DNA type is designated as TH01 6,8.
S
evidence. Only the equivalent of 18 DNA-containing cells is needed to obtain a DNA profile.
H
For instance, STR profiles have been used to identify the origin of saliva residue on envelopes,
stamps, soda cans, and cigaretteA
butts.
To understand the utility of STRs in forensic science, let’s look at one commonly used STR
N
known as TH01. This DNA segment contains the repeating sequence A–A–T–G. Seven TH01
variants have been identified inNthe human genome. These variants contain 5 to 11 repeats of
A–A–T–G. Figure 15–8 illustrates two such TH01 variants, one containing 6 repeats and the
O
other containing 8 repeats of A–A–T–G.
N TH01 is extracted from biological materials and amplified
During a forensic examination,
by PCR as described earlier. The ability to copy an STR means that extremely small amounts of
the molecule can be detected and analyzed. Once the STRs have been copied or amplified, they
1 Here, the STRs are forced to move across a gel-coated plate
are separated by electrophoresis.
under the influence of an electrical
9 potential. Smaller DNA fragments move along the plate faster
than do larger DNA fragments. By examining the distance the STR has migrated on the electro0 the number of A–A–T–G repeats in the STR. Every person has
phoretic plate, one can determine
two STR types for TH01, one inherited
from each parent. Thus, for example, one may find in a
9
semen stain TH01 with six repeats and eight repeats. This combination of TH01 is found in apT
proximately 3.5 percent of the population.
It is important to understand that all humans have the
same type of repeats, but there is
tremendous
variation in the number of repeats each of us has.
S
When examining an STR DNA pattern, one merely needs to look for a match between
band sets. For example, in Figure 15–9 DNA extracted from a crime-scene stain matches the
DNA recovered from one of three suspects. When comparing only one STR, a limited number
of people in a population would have the same STR fragment pattern as the suspect. However,
by using additional STRs, a high degree of discrimination or complete individualization can
be achieved.
multiplexing
A technique that simultaneously
detects more than one DNA
marker in a single analysis.
What makes STRs so attractive to forensic scientists is that hundreds of types of STRs are found
in human genes. The more STRs one can characterize, the smaller the percentage of the population from which these STRs can emanate. This gives rise to the concept of multiplexing. Using
PCR technology, one can simultaneously extract and amplify a combination of different STRs.
Criminalistics: An Introduction to Forensic Science, Eleventh Edition, by Richard Saferstein. Published by Prentice Hall. Copyright © 2015 by Pearson Education, Inc.
ISBN: 978-1-323-16745-8
Multiplexing
DNA: THE INDISPENSABLE FORENSIC SCIENCE TOOL
387
FIGURE 15–9
A DNA profile pattern of
a suspect and its match to
crime-scene DNA. From left to
right, lane 1 is a DNA standard
marker; lane 2 is the crimescene DNA; and lanes 3 to 5 are
control samples from suspects
1, 2, and 3, respectively. Crimescene DNA matches suspect #2.
M
I
L
E
S
,
9
0 probabilities of
The 13 CODIS STRs are listed in Table 15–1 along with their
identity. The probability of identity is a measure of the likelihood
9 that two individuals selected at random will have an identical STR type. The smaller the value
T of discriminaof this probability, the more discriminating the STR. A high degree
tion and even individualization can be attained by analyzing a combination
of STRs
S
Questioned
stain
Control
stain
FGA
vWA
Size Markers
One STR system on the commercial market is the STR Blue Kit. This kit provides
the necessary materials for amplifying and detecting three STRs (a process called
triplexing): D3S1358, vWA, and FGA. The design of the system ensures
S that the size
of the STRs does not overlap, thereby allowing each marker to be viewed clearly on an
H
electrophoretic gel, as shown in Figure 15–10. In the United States, the forensic science
A known as the
community has standardized 13 STRs for entry into a national database
Combined DNA Index System (CODIS).
N
When an STR is selected for analysis, not only must the identity and number
of core repeats be defined, but the sequence of bases flankingNthe repeats must
also be known. This knowledge allows commercial manufacturers of STR typing
O
kits to prepare the correct primers to delineate the STR segment to be amplified
N will be used to
by PCR. Also, a mix of different primers aimed at different STRs
simultaneously amplify a multitude of STRs (i.e., to multiplex). In fact, one STR
kit on the commercial market can simultaneously make copies of 15 different STRs
1
(see Figure 15–11).
ISBN: 978-1-323-16745-8
DNA Typing with STRs
(multiplexing). Because STRs occur independently of each other, the probability of
biological evidence having a particular combination of STR types is determined by
the product of their frequency of occurrence in a population. This combination is
referred to as the product rule (see page 64). Hence, the greater the number of STRs
characterized, the smaller the frequency of occurrence of the analyzed sample in the
general population.
The combination of the first 3 STRs shown in Table 15–1 typically produces
a frequency of occurrence of about 1 in 5,000. A combination of the first 6 STRs
typically yields a frequency of occurrence in the range of one in two million for the
Caucasian population, and if the top 9 STRs are determined in combination, this frequency declines to about one in one billion. The combination of all 13 STRs shown
in Table 15–1 typically produces frequencies of occurrence that measure in the
D3S1358
FIGURE 15–10
A triplex system containing three loci:
FGA, vWA, and D3S1358, indicating a
match between the questioned and the
standard/reference stains.
Criminalistics: An Introduction to Forensic Science, Eleventh Edition, by Richard Saferstein. Published by Prentice Hall. Copyright © 2015 by Pearson Education, Inc.
CHAPTER 15
FIGURE 15–11
STR profile for 15 loci.
M
I
L
E
S
,
Richard Saferstein
388
S
H
TABLE 15–1
A
The 13 CODIS STRs and Their Probability of Identities
N
STR
NAfrican American
D3S1358
0.094
O
vWA
0.063
N
FGA
0.033
TH01
TPOX
CSF1PO
D5S818
D13S317
D7S820
D8S1179
D21S11
D18S51
D16S539
1
9
0
9
T
S
0.109
0.090
0.081
0.112
0.136
0.080
0.082
0.034
0.029
0.070
U.S. Caucasian
0.075
0.062
0.036
0.081
0.195
0.112
0.158
0.085
0.065
0.067
0.039
0.028
0.089
Source: The Future of Forensic DNA Testing: Predictions of the Research and Development Working Group.
Washington, D.C.: National Institute of Justice, Department of Justice, 2000, p. 41.
WEBEXTRA 15.4
range of 1 in 575 trillion for Caucasian Americans and 1 in 900 trillion for African Americans.
Importantly, several commercially available kits allow forensic scientists to profile STRs in the
kinds of combinations cited here.
Sex Identification Using STRs
amelogenin gene
A genetic locus useful for
determining gender.
Manufacturers of commercial STR kits typically used by crime laboratories provide one additional piece of useful information along with STR types: the sex of the DNA contributor. The
focus of attention here is the amelogenin gene located on both the X and Y chromosomes. This
Criminalistics: An Introduction to Forensic Science, Eleventh Edition, by Richard Saferstein. Published by Prentice Hall. Copyright © 2015 by Pearson Education, Inc.
ISBN: 978-1-323-16745-8
Understand the Operational
Principles of Capillary
Electrophoresis
DNA: THE INDISPENSABLE FORENSIC SCIENCE TOOL
gene, which is actually the gene for tooth pulp, has an interesting characteristic in that it is shorter
by six bases in the X chromosome than in the Y chromosome. Hence, when the amelogenin gene
is amplified by PCR and separated by electrophoresis, males, who have an X and a Y chromosome, show two bands; females, who have two X chromosomes, have just one band. Typically,
these results are obtained in conjunction with STR types.
Another tool in the arsenal of the DNA analyst is the ability to type STRs located on the
Y chromosome. The Y chromosome is male specific and is always paired with the X chromosome. Although more than 400 Y-STRs have been identified, only a small number of them
are being used for forensic applications. One commercial kit allows for the characterization of
17 Y chromosome STRs. When can it be advantageous to seek out Y-STR types? Generally,
Y-STRs are useful for analyzing blood, saliva, or a vaginal swab that is a mix originating from
more than one male. For example, Y-STRs prove useful when multiple males are involved in a
sexual assault. Further simplifying the analysis is that any DNA in the mixture that originates
from a female will not show.
Keep in mind that STR types derived from the Y chromosome originate only from this
M
single male chromosome. A female subject, or one with an XX chromosome pattern, does not
contribute any DNA information. Also, unlike a conventional STR
I type that is derived from two
chromosomes and typically shows two bands or peaks, a Y-STR has only one band or peak for
L
each STR type.
For example, the traditional STR DNA pattern may prove toEbe overly complex in the case
of a vaginal swab containing the semen of two males. Each STR type would be expected to show
S
four bands, two from each male. Also complicating the appearance of the DNA profile may be
the presence of DNA from skin cells emanating from the walls, of the vagina. In this circumstance, homing in on the Y chromosome greatly simplifies the appearance and interpretation
of the DNA profile. Thus, when presented with a DNA mixture of two males and one female,
Y-STR analysis would show only two bands (one band for each S
male) for each Y-STR type.
When gauging the significance of a Y-STR match between questioned and known speciH
mens, one should take into consideration that all male paternal relatives (e.g., brothers, father,
male offspring, and uncles) would be expected to have the same A
Y-STR profile.
Another advantage of employing STR technology is to extendN
the success of detecting evidential DNA from vaginal swabs collected from rape victims. Casework experience has demonstrated
significant difficulties in obtaining traditional STR DNA profiles N
for the male donor from vaginal
swabs collected after three to four days after intercourse. However,O
the application of Y-STR technology often extends the routine postcoital detection time to five days for the male donor.
389
Y-STRs
Short tandem repeats located on
the human Y chromosome.
N
1
9
0
9
T high-voltage energy. The column is coated with a gel
polymer, and the DNA-containing sample solution is
S injected into one end of the column by applying a
inside the science
ISBN: 978-1-323-16745-8
Capillary Electrophoresis
The separation of STRs can typically be carried out on
a flat gel-coated electrophoretic plate, as described
earlier. However, the need to reduce analysis time and
to automate sampling and data collection has led to
the emergence of capillary electrophoresis as the preferred technology for characterization of STRs. Capillary electrophoresis is carried out in a thin glass column
rather than on the surface of a coated-glass plate.
As illustrated in the figure, each end of the column is immersed in a reservoir of buffer liquid that
also holds electrodes (coated with platinum) to supply
high voltage to an electrode immersed in the DNA
solution. The STR fragments then move through the
column under the influence of an electrical potential
at a speed that is related to the length of the STR
fragments. The other end of the column is connected
to a detector that tracks the separated STRs as they
emerge from the column. As the DNA peaks pass
through the detector, they are recorded on a display known as an electropherogram, as shown in the
figure.
(continued )
Criminalistics: An Introduction to Forensic Science, Eleventh Edition, by Richard Saferstein. Published by Prentice Hall. Copyright © 2015 by Pearson Education, Inc.
390
CHAPTER 15
Electrical potential
is applied to STR
fragments in column
Voltage supply
Fragments move at different
speeds through column under
influence of electric potential
Sample containing
DNA is injected
into capillary
column
Capillary
column
Injection
Area
M
I
Detector
L
Platinum-coated E
electrodes
S
,
(a)
S
H
A
N
Detector tracks separated
N STRs
as they emerge from column
O
N
Voltage supply
Injection
Area
Capillary column
1
9
0
Detector
9
T
S
Electropherogram
recorder shows
separation pattern
of STRs
(b)
Criminalistics: An Introduction to Forensic Science, Eleventh Edition, by Richard Saferstein. Published by Prentice Hall. Copyright © 2015 by Pearson Education, Inc.
ISBN: 978-1-323-16745-8
Capillary electrophoresis technology has evolved from the traditional flat gel electrophoresis approach. The separation of DNA
segments is carried out on the interior wall of a glass capillary tube that is kept at a constant voltage. The size of the DNA fragments
determines the speed at which they move through the column. This figure illustrates the separation of three sets of STRs (triplexing).
DNA: THE INDISPENSABLE FORENSIC SCIENCE TOOL
391
inside the science
MiniSTRs
The forensic science community turned to STRs when
it became apparent that short segments of DNA
would be required to meet the requirements of PCR.
Commercial manufacturers of DNA-typing kits prepared a series of 13 STRs for compatibility with the
CODIS DNA database that ranged in length from 100
to 450 bases. One obvious benefit in working with
short DNA segments was the likelihood that useful information could be extracted even from fragmented
DNA. This often proved to be the case, but not always. On occasion, degraded DNA is encountered
that is so badly damaged that traditional STR analysis
is not possible. Prolonged exposure of DNA to extreme environmental elements, such as temperature
extremes, humidity, or microbial activity, can lead to
such degradation. An approach to dealing with this
problem is to further shorten the STR strands that
emerge from the PCR process.
The approach that has been taken to accomplish this task is to create new primers that can be
positioned closer to the STR repeat region (see the
figure). The shorter STR products (called amplicons)
that now emerge from PCR increase the chances of
C
C
A
G
G
G
T
C
Primer
G
G
T
C
characterizing badly fragmented strands of DNA.
These smaller amplicons are called “miniSTRs.” One
manufacturer of STR kits has produced a miniSTR kit
designed to amplify eight miniSTRs, seven of which
are totally compatible with the CODIS database. The
miniSTRs range in size from 71 to 250 bases. A DNA
analyst suspecting a degraded sample now has the
option, if sample size permits, of running both traditional STR and miniSTR determinations, or just the
latter.
The advent of miniSTRs means that forensic scientists
can now analyze samples that were once
M
thought to be of no value. One of the first benefacI tors of miniSTR technology was the identification of
L a number of victims from the Waco Branch Davidian
fire. Also, a number of World Trade Center victims
E were identified by miniSTR technology. Another foS cus of attention has been human hair. In the past, exnuclear DNA out of the hair shaft has been
, tracting
enormously difficult; the number of STRs in hair has
been found to be very low as well as highly degraded.
one study has demonstrated that miniSTRs
S However,
may overcome some of the difficulties in obtaining
H partial profiles from the degraded DNA present in
shed hair.2
A
N
N
O
N
A
T
T
C
A
T
T
C
T
A
A
G
Primer
1 units of a DNA segment in order to
Appropriate primers are positioned close to the repeat
initiate the PCR process that will create short or9
mini STRs.
ISBN: 978-1-323-16745-8
0
9
T
Significance of DNA Typing
STR DNA typing has become an essential and basic investigative
S tool in the law enforcement
community. The technology has progressed at a rapid rate and in only a few years has surmounted
numerous legal challenges to become vital evidence for resolving violent crimes and sex offenses. DNA evidence is impartial, implicating the guilty and exonerating the innocent.
In a number of well-publicized cases, DNA evidence has exonerated individuals who have
been wrongly convicted and imprisoned. The importance of DNA analyses in criminal investigations has also placed added burdens on crime laboratories to improve their quality-assurance
procedures and to ensure the correctness of their results. In several well-publicized instances,
the accuracy of DNA tests conducted by government-funded laboratories has been called into
question.
2
WEBEXTRA 15.5
See the 13 CODIS STRs and Their
Chromosomal Positions
WEBEXTRA 15.6
See How to Calculate the Frequency
of Occurrence of a DNA Profile
WEBEXTRA 15.7
See the Electropherogram Record
from One Individual’s DNA
WEBEXTRA 15.8
An Animation Depicting Y-STRs
K. E. Opel et al., “Evaluation and Quantification of Nuclear DNA from Human Telogen Hairs,” Journal of Forensic
Sciences 53 (2008): 853.
Criminalistics: An Introduction to Forensic Science, Eleventh Edition, by Richard Saferstein. Published by Prentice Hall. Copyright © 2015 by Pearson Education, Inc.
392
CHAPTER 15
The Combined DNA
Index System (CODIS)
Perhaps the most significant investigative tool to arise from a DNA-typing program is CODIS
(Combined DNA Index System), a computer software program developed by the FBI that maintains local, state, and national databases of DNA profiles from convicted offenders, unsolved
crime-scene evidence, and profiles of missing people. CODIS allows crime laboratories to compare DNA types recovered from crime-scene evidence to those of convicted sex offenders and
other convicted criminals.
Thousands of CODIS matches have linked serial crimes to each other and have solved
crimes by allowing investigators to match crime-scene evidence to known convicted offenders.
This capability is of tremendous value to investigators in cases in which the police have not been
able to identify a suspect. The CODIS concept has already had a significant impact on police
investigations in various states, as shown in the Case Files feature on page 70.
M
I
Mitochondrial DNA
Typically, when one describes L
DNA in the context of a criminal investigation, the subject is
assumed to be the DNA in theE
nucleus of a cell. Actually, a human cell contains two types of
DNA—nuclear and mitochondrial. The first constitutes the 23 pairs of chromosomes in the nuclei
S
of our cells. Each parent contributes to the genetic makeup of these chromosomes. Mitochondrial
DNA (mtDNA), on the other hand,
, is found outside the nucleus of the cell and is inherited solely
mitochondria
Small structures located outside
the nucleus of a cell; these structures supply energy to the cell;
maternally inherited DNA is found
in each mitochondrion.
from the mother.
Mitochondria are cell structures found in all human cells. They are the power plants of
the body, providing about 90 percent
of the energy that the body needs to function. A single
S
mitochondrion contains several loops of DNA, all of which are involved in energy generation.
H
Further, because each cell in our bodies contains hundreds to thousands of mitochondria, there
are hundreds to thousands of mtDNA
A copies in a human cell. This compares to just one set of
case files
N
N
O
N
Cold Case Hit
1
Source: National Institute of Justice, “Using DNA to Solve Cold Cases”
(NIJ Special Report), July 2002.
Criminalistics: An Introduction to Forensic Science, Eleventh Edition, by Richard Saferstein. Published by Prentice Hall. Copyright © 2015 by Pearson Education, Inc.
ISBN: 978-1-323-16745-8
In 1990, a series of attacks on elderly victims was committed in
Goldsboro, North Carolina, by an unknown individual dubbed9
the Night Stalker. During one such attack in March, an elderly
0
woman was brutally sexually assaulted and almost murdered.
Her daughter’s early arrival home saved the woman’s life. The9
suspect fled, leaving behind materials intended to burn the resiT
dence and the victim in an attempt to conceal the crime.
In July 1990, another elderly woman was sexually as-S
saulted and murdered in her home. Three months later, a third
elderly woman was sexually assaulted and stabbed to death.
Her husband was also murdered. Although their house was set
alight in an attempt to cover up the crime, fire and rescue personnel pulled the bodies from the house before it was engulfed
in flames. DNA analysis of biological evidence collected from
vaginal swabs from the three sexual assault victims enabled authorities to conclude that the same perpetrator had committed
all three crimes. However, there was no suspect.
More than ten years after these crimes were committed,
law enforcement authorities retested the biological evidence
from all three cases using newer DNA technology and entered
the DNA profiles into North Carolina’s DNA database. The
DNA profile developed from the crime-scene evidence was
compared to thousands of convicted-offender profiles already
in the database.
In April 2001, a “cold hit” was made: The DNA profiles
was matched to that of an individual in the convicted-offender
DNA database. The perpetrator had been convicted of shooting
into an occupied dwelling, an offense that requires inclusion of
the convict’s DNA in the North Carolina DNA database. The
suspect was brought into custody for questioning and was served
with a search warrant to obtain a sample of his blood. That sample was analyzed and compared to the crime-scene evidence,
confirming the DNA database match. When confronted with the
DNA evidence, the suspect confessed to all three crimes.
DNA: THE INDISPENSABLE FORENSIC SCIENCE TOOL
393
inside the science
Familial DNA—Expanding
the DNA Database
In 1984, Deborah Sykes was raped and stabbed to
death as she walked to work in Winston-Salem, North
Carolina. A month later, Darryl Hunt, then 19 years old,
was arrested and eventually convicted of the crime.
Hunt insisted that he was innocent, and by 1990, DNA
testing of semen found on Sykes proved that he was
not its source. Nevertheless, North Carolina prosecutors ignored this new evidence and he remained in
jail. Finally, a search against Darryl Hunt’s STR profile
in the North Carolina DNA database revealed a close
but not perfect match to a genetic profile already in
the database, that of his brother. Upon further investigation, that man, Willard Brown, confessed to
Sykes’s murder in 2003, and Hunt was finally freed
from prison.
In this case, DNA profiling exonerated an innocent man and helped lead the police to the real culprit. The Sykes case illustrates how the contents of a
criminal DNA database can be dramatically expanded
to aid the police in identifying criminals by searching
the database for near matches.
Typically, the CODIS database is used to find exact matches with crime-scene DNA. However, taking
into account the facts that the 13 STR loci that constitute U.S. offender DNA databases are genetically
inherited and that each individual’s DNA profile is genetically determined by one’s parents creates opportunities to use the database’s raw data to search out
close relatives. DNA profiles of related individuals are
likely to show a higher proportion of shared STR loci as
compared to unrelated individuals. Hence, searching
the database for profiles that have a high degree of
commonality may lead to the identification of a close
relative of the perpetrator. Interestingly, studies have
shown that a person’s chances of committing a crime
increase if a parent or sibling had previously done so.
A 1999 U.S. Department of Justice survey found that
46 percent of jail inmates had at least one close relative who had also been incarcerated.
The potential for improving the effectiveness
of DNA database searches is considerable. Familial
searches of a DNA database would dramatically increase the size of the database by three or more times
M because every profile that is entered would, in effect,
I contain genetic information about the STR alleles of
the donor’s parents, siblings, and children. One study
L estimates that using familial DNA searches could inE crease the “cold hit” rates by 40 percent. Considering
fact that there have been about 95,000 cold hits in
S the
the United States, familial DNA has the potential for
, identifying thousands of additional criminal suspects.
The concept of familial DNA searching has been
routinely adopted in the United Kingdom. In the
S United States, the FBI notifies investigators about
matches it finds using its current software, but
H close
the agency has no current plans to modify its search
A algorithms to optimize the database’s capacity to ferout near or close matches. This leaves it up to the
N ret
states to decide whether to release identifying inforN mation about an offender whose DNA closely matches
sample from another state. Challengers
O atocrime-scene
familial database searching have cited it as a violaN tion of constitutional protections against unreasonable
search and seizure. A number of mixed state court decisions have failed to produce a consensus on the con1 stitutionality of familial DNA database searches.
ISBN: 978-1-323-16745-8
9
0
9
nuclear DNA located in that same cell. Thus, forensic scientists are offered enhanced sensitivity
T
and the opportunity to characterize mtDNA when nuclear DNA is significantly degraded, such
as in charred remains, or when nuclear DNA may be present inSa small quantity (such as in a
hair shaft). Interestingly, when authorities cannot obtain a reference sample from an individual
who may be long deceased or missing, an mtDNA reference sample can be obtained from any
maternally related relative. However, all individuals of the same maternal lineage will be indistinguishable by mtDNA analysis.
Although mtDNA analysis is significantly more sensitive than nuclear DNA profiling, forensic analysis of mtDNA is more rigorous, time consuming, and costly than nuclear DNA profiling. For this reason, only a handful of public and private forensic laboratories receive evidence
for this type of determination. The FBI Laboratory has imposed strict limitations on the types of
cases in which it will apply mtDNA technology.
sequencing
A procedure used to determine
the order of the base pairs that
constitute DNA.
Criminalistics: An Introduction to Forensic Science, Eleventh Edition, by Richard Saferstein. Published by Prentice Hall. Copyright © 2015 by Pearson Education, Inc.
394
CHAPTER 15
inside the science
Forensic Aspects
of Mitochondrial DNA
As was previously discussed, nuclear DNA is composed of a continuous linear strand of nucleotides
(A, T, G, and C). On the other hand, mtDNA is constructed in a circular or loop configuration. Each loop
contains enough A, T, G, and C (approximately 16,569
units) to make up 37 genes involved in mitochondrial
energy generation. Two regions of mtDNA have been
found to be highly variable in the human population.
These two regions have been designated hypervariable region I (HV1) and hypervariable region II (HV2),
as shown in the figure. As indicated previously, the process for analyzing HV1 and HV2 is tedious. It involves
generating many copies of these DNA hypervariable
regions by PCR and then determining the order of
the A–T–G–C bases constituting the hypervariable
regions. This process is known as sequencing. The
FBI Laboratory, the Armed Forces DNA Identification
H
A
N
N
O
Mitochondria
N
CELL
Nucleus
Control Region
HV1
Laboratory, and other laboratories have collaborated
to compile an mtDNA population database containing the base sequences from HV1 and HV2.
Once the sequences of the hypervariable regions
from a case sample are obtained, most laboratories
simply report the number of times these sequences
appear in the mtDNA database maintained by the FBI.
The mtDNA database contains about five thousand
sequences. This approach permits an assessment of
Mhow common or rare an observed mtDNA sequence is
I in the database. Interestingly, many of the sequences
that have been determined in casework are unique
Lto the existing database, and many types are present
Eat frequencies no greater than 1 percent in the database. Thus it is often possible to demonstrate how unScommon a particular mitochondrial DNA sequence is.
, However, even under the best circumstances, mtDNA
typing does not approach STR analysis in its discrimination power. Thus, mtDNA analysis is best reserved
Sfor samples for which nuclear DNA typing is simply
not possible.
HV2
1
9
0
9
T
S
Mitochondrial DNA
Criminalistics: An Introduction to Forensic Science, Eleventh Edition, by Richard Saferstein. Published by Prentice Hall. Copyright © 2015 by Pearson Education, Inc.
ISBN: 978-1-323-16745-8
Every cell in the body contains hundreds of mitochondria, which provide energy to the cell. Each mitochondrion contains numerous
copies of DNA shaped in the form of a loop. Distinctive differences between individuals in their mitochondrial DNA makeup are
found in two specific segments of the control region on the DNA loop known as HV1 and HV2.
DNA: THE INDISPENSABLE FORENSIC SCIENCE TOOL
Collection and Preservation of Biological
Evidence for DNA Analysis
WEBEXTRA 15.9
Since the early 1990s, the advent of DNA profiling has vaulted biological crime-scene evidence to a stature of importance that is eclipsed only by the fingerprint. In fact, the high sensitivity of DNA determinations has even changed the way police investigators define biological
evidence.
Just how sensitive is STR profiling? Forensic analysts using currently accepted protocols
can reach sensitivity levels as low as 125 picograms. Interestingly, a human cell has an estimated
7 picograms of DNA, which means that only 18 DNA-bearing cells are needed to obtain an STR
profile. However, modifications in the technology can readily extend the level of detection down
to 9 cells. A quantity of DNA that is below the normal level of detection is defined as a low copy
number. (However, analysts must take extraordinary care in analyzing low-copy-number DNA
and often may find that courts will not allow this data to be admissible in a criminal trial.) With
this technology in hand, the horizon of the criminal investigatorM
extends beyond the traditional
dried blood or semen stain to include stamps and envelopes licked with saliva, a cup or can that
I or a bedsheet containing dead
has touched a person’s lips, chewing gum, the sweat band of a hat,
skin cells. Likewise, skin or epithelial cells transferred onto the surface
L of a weapon, the interior
of a glove, or a pen have yielded DNA results.3
The phenomenon of transferring DNA via skin cells onto theEsurface of an object has come
to be called touch DNA. Again, keep in mind that, in theory, only
S 18 skin cells deposited on an
object are required to obtain a DNA profile.
WEBEXTRA 15.10
,
Collection of Biological Evidence
S of DNA, they should first
However, before investigators become enamored with the wonders
realize that the crime scene must be treated in the traditional manner.
H Before the collection of
evidence begins, biological evidence should be photographed close up and its location relative to
A
the entire crime scene recorded through notes, sketches, and photographs.
If the shape and position of bloodstains may provide information about the circumstances
of
the
crime, an expert must
N
immediately conduct an on-the-spot evaluation of the blood evidence. The significance of the
position and shape of bloodstains can best be ascertained when theNexpert has an on-site overview
of the entire crime scene and can better reconstruct the movement
O of the individuals involved.
No attempt should be made to disturb the blood pattern before this phase of the investigation is
N
completed.
The evidence collector must handle all body fluids and biologically stained materials with a
minimum amount of personal contact. All body fluids must be assumed to be infectious; hence,
1
wearing disposable latex gloves while handling the evidence is required.
Latex gloves also significantly reduce the possibility that the evidence collector will contaminate
the evidence. These
9
gloves should be changed frequently during the evidence-collection phase of the investigation.
Safety considerations and avoidance of contamination also call 0
for the wearing of face masks,
a lab coat, eye protection, shoe covers, and possibly coveralls. 9
The deposition of DNA onto crime-scene objects via saliva, sweat, skin, blood, and semen
T from the traditional evidence
has created a vast array of forensic evidence that is quite different
collected at crime scenes prior to the DNA era (see Table 15–2).S
395
See How We Inherit Our
Mitochondrial DNA
Look into the Structure of Mitochondrial DNA and See How It Is
Used for DNA Typing
picogram
One-trillionth of a gram, or
0.000000000001 gram.
low copy number
Fewer than 18 DNA-bearing cells.
epithelial cells
The outer layer of skin cells; these
DNA-bearing cells often fall off
or are rubbed off onto objects retrieved from crime scenes.
touch DNA
DNA from skin cells transferred
onto the surface of an object by
simple contact.
ISBN: 978-1-323-16745-8
Packaging of Biological Evidence
Biological evidence should not be packaged in plastic or airtight containers because accumulation of residual moisture could contribute to the growth of DNA-destroying bacteria and fungi.
Each stained article should be packaged separately in a paper bag or a well-ventilated box.
A red-bio-hazard label must be attached to each container. If feasible, the entire stained article
3
R. A. Wickenheiser, “Trace DNA: A Review, Discussion of Theory, and Application of the Transfer of Trace Qualities through Skin Contact,” Journal of Forensic Sciences 47 (2002): 442.
Criminalistics: An Introduction to Forensic Science, Eleventh Edition, by Richard Saferstein. Published by Prentice Hall. Copyright © 2015 by Pearson Education, Inc.
396
CHAPTER 15
TABLE 15–2
Location and Sources of DNA at Crime Scenes
substrate control
Possible Location
of DNA on the Evidence
Baseball bat or similar weapon
Hat, bandanna, mask
Eyeglasses
Facial tissue, cotton swab
Handle, end
Inside
Nose or ear pieces, lens
Surface area
Dirty laundry
Toothpick
Used cigarette
Stamp or envelope
Tape or ligature
Bottle, can, glass
Used condom
Surface area
Tips
Cigarette butt
Licked area
Inside/outside surface
Sides, mouthpiece
Inside/outside surface
M
I
L
Blanket, pillow, sheet
E
“Through and through” bulletS
Bite mark
,
Fingernail, partial fingernail
buccal cells
Cells derived from the inner cheek
lining.
Outside surface
Person’s skin or clothing
Scrapings
Sweat, skin, blood, tissue
Sweat, hair, dandruff
Sweat, skin
Mucus, blood, sweat,
semen, ear wax
Blood, sweat, semen
Saliva
Saliva
Saliva
Skin, sweat
Saliva, sweat
Semen, vaginal or
rectal cells
Sweat, hair, semen,
urine, saliva
Blood, tissue
Saliva
Blood, sweat, tissue
S
H
should be packaged and submitted for examination. If this is not possible, dried
blood is best A
removed from a surface with a sterile cotton-tipped swab lightly
moistened with
N distilled water from a dropper bottle. A portion of the unstained
surface material near the recovered stain must likewise be removed or swabbed
and placed inNa separate package. This is known as a substrate control. The
forensic examiner
O may use the substrate swab to confirm that the results of
the tests performed were brought about by the stain and not by the material on
which it was N
deposited. However, this practice is normally not necessary when
DNA determinations are carried out in the laboratory. One point is critical, and
that is that the collected swabs must not be packaged in a wet state. After the
collection is 1
made, the swab must be air-dried for approximately five to ten
minutes. Then9it is best to place it in a swab box (see Figure 15–12), which has
a circular hole to allow air circulation. The swab box can then be placed in a
0 envelope.
paper or manila
All packages
9 containing biological evidence should be refrigerated or
stored in a cool location out of direct sunlight until delivery to the laboratory.
However, oneTcommon exception is blood mixed with soil. Microbes present
in soil rapidlySdegrade DNA. Therefore, blood in soil must be stored in a clean
glass or plastic container and immediately frozen.
Obtaining DNA Reference Specimens
Biological evidence attains its full forensic value only when an analyst can
compare each of its DNA types to known DNA samples collected from victims and suspects.
The least intrusive method for obtaining a DNA standard/reference, one that nonmedical personnel can readily use, is the buccal swab. Cotton swabs are placed in the subject’s mouth and
the inside of the cheek is vigorously swabbed, resulting in the transfer of buccal cells onto the
swab (see Figure 15–13).
If an individual is not available to give a DNA standard/reference sample, some interesting
alternatives are available to evidence collectors, including a toothbrush, combs and hairbrushes,
Criminalistics: An Introduction to Forensic Science, Eleventh Edition, by Richard Saferstein. Published by Prentice Hall. Copyright © 2015 by Pearson Education, Inc.
ISBN: 978-1-323-16745-8
FIGURE 15–12
Air-dried swabs are placed
in a swab box for delivery
to the forensic laboratory.
Surface area
Source of DNA
Source: National Institute of Justice, U.S. Department of Justice.
Courtesy of Tri-Tech Forensics, Inc., Southport, NC
An unstained object adjacent to an
area on which biological material
has been deposited.
Evidence
DNA: THE INDISPENSABLE FORENSIC SCIENCE TOOL
397
a razor, soiled laundry, used cigarette butts, and earplugs. Any of these items may contain a sufficient quantity of DNA for typing purposes. Interestingly, as investigators worked to identify the
remains of victims of the World Trade Center attack on September 11, 2001, the families of the
missing were requested to supply the New York City DNA Laboratory with these types of items
in an effort to match recovered DNA with human remains.
M
I
L
E
S
,
ISBN: 978-1-323-16745-8
1
9
0
9
T
S
Courtesy of Tri-Tech Forensics, Inc., Southport, NC
S
H
A
N
N
O
N
FIGURE 15–13
A buccal swab collection kit is designed for use by nonmedical personnel. The
cotton-tipped swabs are placed in the subject’s mouth and the inside of the cheek is
vigorously swabbed, resulting in the transferr of buccal cells onto the cotton bulb of
the swab. The kit is then delivered to the forensic laboratory.
Criminalistics: An Introduction to Forensic Science, Eleventh Edition, by Richard Saferstein. Published by Prentice Hall. Copyright © 2015 by Pearson Education, Inc.
398
CHAPTER 15
Contamination of DNA Evidence
One key concern during the collection of a DNA-containing specimen is contamination. Contamination can occur by introducing foreign DNA through coughing or sneezing onto a stain during
the collection process, or there can be a transfer of DNA when items of evidence are incorrectly
placed in contact with each other during packaging. Fortunately, an examination of DNA band
patterns in the laboratory readily reveals the presence of contamination. For example, with an
STR, one will expect to see a two-band pattern. More than two bands suggest a mixture of DNA
from more than one source.
Crime-scene investigators can take some relatively simple steps to minimize contamination
of biological evidence:
1. Use disposable gloves.
2. Wear a face mask while collecting evidence, a lab coat, eye protection, as well as shoe
covers.
3. Change gloves before handling each new piece of evidence.
4. Collect a substrate control M
for possible subsequent laboratory examination.
5. Pick up small items of evidence
I such as cigarette butts and stamps with clean forceps. Disposable forceps are to be used so that they can be discarded after a single evidence collection.
6. Always package each itemL
of evidence in its own well-ventilated container.
WEBEXTRA 15.11
E scenes is to suspect the presence of blood but not be able
A common occurrence at crime
to observe any with the naked eye.
S In these situations, the common test of choice is luminol or
Bluestar (see page 363). Interestingly, neither luminol nor Bluestar is expected to inhibit the
,
ability to detect and characterize STRs.4 Therefore, luminol and Bluestar can be used to locate
traces of blood and areas that have been washed nearly free of blood without compromising the
potential for DNA typing.
Step into the Role of the First
Responding Officer at a Burglary
Scene
WEBEXTRA 15.12
case files
Assume the Duties of an Evidence
Collection Technician at a Burglary
Scene
S
H
A
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Contact Lens Evidence
N
A woman alleged that she had been held against her will andO
sexually assaulted by a male friend in an apartment. During the
course of the assault, a contact lens was knocked from the vic-N
tim’s eye. After the assault, she escaped, but because she was
afraid of the threats made by her attacker, she did not report the
assault to the police for three days. When the police examined1
the apartment, they noted that it had been thoroughly cleaned.
A vacuum cleaner bag was seized for examination, and several9
pieces of material resembling fragments of a contact lens were
discovered within the bag.
In the laboratory, approximately 20 nanograms of human
DNA was recovered from the contact lens fragments. Cells from
both the eyeball and the interior of the eyelids are naturally replaced every 6 to 24 hours. Therefore, both are potential sources
for the DNA found. The DNA profile originating from the fragments matched the victim, thus corroborating the victim’s account
of the crime. The estimated population frequency of occurrence
for the nine matching STRs are approximately 1 in 850 million.
The suspect subsequently pleaded guilty to the offense.
STR Locus
0 Type
Victim’s DNA
Contact Lens
D3S1358
FGA
vWA
TH01
F13A1
fes/fps
D5S818
D13S317
D7S820
15,918
24, 25
T
17, 17
6,S7
5, 6
11, 12
11, 12
11, 12
10, 12
15, 18
24, 25
17, 17
6, 7
5, 6
11, 12
11, 12
11, 12
10, 12
4
A. M. Gross et al., “The Effect of Luminol on Presumptive Tests and DNA Analysis Using the Polymerase Chain
Reaction,” Journal of Forensic Sciences 44 (1999): 837.
Criminalistics: An Introduction to Forensic Science, Eleventh Edition, by Richard Saferstein. Published by Prentice Hall. Copyright © 2015 by Pearson Education, Inc.
ISBN: 978-1-323-16745-8
Based on information in R. A. Wickenheiser and R. M. Jobin, “Comparison
of DNA Recovered from a Contact Lens Using PCR DNA Typing,” Canadian Society
of Forensic Science Journal 32 (1999): 67.
ISBN: 978-1-323-16745-8
case files
DNA: THE INDISPENSABLE FORENSIC SCIENCE TOOL
The JonBenét Ramsey
Murder Case
Point–Counterpoint
Point
July 9, 2008
Boulder District Attorney Mary T. Lacy issues the following
announcement with regard to the investigation of the murder
of JonBenét Ramsey.
On December 25–26, 1996, JonBenét Ramsey was murdered in the home where she lived with her mother, father and
M
brother. Despite a long and intensive investigation, the death of
I
JonBenét remains unsolved.
The murder has received unprecedented publicity and has
L
been shrouded in controversy. That publicity has led to many
theories over the years in which suspicion has focused on one
E
family member or another. However, there has been at least
S
one persistent stumbling block to the possibility of prosecuting
any Ramsey family members for the death of JonBenét—DNA.
,
As part of its investigation of the JonBenét Ramsey homicide, the Boulder Police identified genetic material with
apparent evidentiary value. Over time, the police continued to
S
investigate DNA, including taking advantage of advances in
the science and methodology. One of the results of their efforts
H
was that they identified genetic material and a DNA profile
A
from drops of JonBenét’s blood located in the crotch of the underwear she was wearing at the time her body was discovered.
N
That genetic profile belongs to a male and does not belong to
anyone in the Ramsey family.
N
The police department diligently compared that profile to
O
a very large number of people associated with the victim, with
her family, and with the investigation, and has not identified the
N
source, innocent or otherwise, of this DNA. The Boulder Police
and prosecutors assigned to this investigation in the past also
worked conscientiously with laboratory analysts to obtain bet1
ter results through new approaches and additional tests as they
became available. Those efforts ultimately led to the discovery
9
of sufficient genetic markers from this male profile to enter it
0
into the national DNA data bank.
In December of 2002, the Boulder District Attorney’s Of9
fice, under Mary T. Lacy, assumed responsibility for the investigation of the JonBenét Ramsey homicide. Since then, this
T
office has worked with the Boulder Police Department to conS
tinue the investigation of this crime.
In early August of 2007, District Attorney Lacy attended a
Continuing Education Program in West Virginia sponsored by the
National Institute of Justice on Forensic Biology and DNA. The presenters discussed successful outcomes from a new methodology described as “touch DNA.” One method for sampling for touch DNA
is the “scraping method.” In this process, forensic scientists scrape a
surface where there is no observable stain or other indication of possible DNA in an effort to recover for analysis any genetic material
that might nonetheless be present. This methodology was not well
known in this country until recently and is still used infrequently.
399
In October of 2007, we decided to pursue the possibility of submitting additional items from the JonBenét Ramsey
homicide to be examined using this methodology. We checked
with a number of Colorado sources regarding which private
laboratory to use for this work. Based upon multiple recommendations, including that of the Boulder Police Department,
we contacted the Bode Technology Group located near
Washington, D.C., and initiated discussions with the professionals at that laboratory. First Assistant District Attorney Peter
Maguire and Investigator Andy Horita spent a full day with
staff members at the Bode facility in early December of 2007.
The Bode Technology laboratory applied the “touch
DNA” scraping method to both sides of the waist area of the
long johns that JonBenét Ramsey was wearing over her underwear when her body was discovered. These sites were chosen
because evidence supports the likelihood that the perpetrator
removed and/or replaced the long johns, perhaps by handling
them on the sides near the waist.
On March 24, 2008, Bode informed us that they had recovered and identified genetic material from both sides of the
waist area of the long johns. The unknown male profile previously identified from the inside crotch area of the underwear
matched the DNA recovered from the long johns at Bode.
We consulted with a DNA expert from a different laboratory, who recommended additional investigation into the remote possibility that the DNA might have come from sources
at the autopsy when this clothing was removed. Additional
samples were obtained and then analyzed by the Colorado
Bureau of Investigation to assist us in this effort. We received
those results on June 27th of this year and are, as a result, confidant that this DNA did not come from innocent sources at
the autopsy. As mentioned above, extensive DNA testing had
previously excluded people connected to the family and to the
investigation as possible innocent sources.
I want to acknowledge my appreciation for the efforts of
the Boulder Police Department, Bode Technology Group, the
Colorado Bureau of Investigation, and the Denver Police Department Forensic Laboratory for the great work and assistance
they have contributed to this investigation.
The unexplained third party DNA on the clothing of the
victim is very significant and powerful evidence. It is very unlikely that there would be an innocent explanation for DNA
found at three different locations on two separate items of clothing worn by the victim at the time of her murder. This is particularly true in this case because the matching DNA profiles were
found on genetic material from inside the crotch of the victim’s
underwear and near the waist on both sides of her long johns,
and because concerted efforts that might identify a source, and
perhaps an innocent explanation, were unsuccessful.
It is therefore the position of the Boulder District Attorney’s
Office that this profile belongs to the perpetrator of the homicide.
DNA is very often the most reliable forensic evidence we
can hope to find during a criminal investigation. We rely on it
often to bring to justice those who have committed crimes. It
can likewise be reliable evidence upon which to remove people
from suspicion in appropriate cases.
(continued )
Criminalistics: An Introduction to Forensic Science, Eleventh Edition, by Richard Saferstein. Published by Prentice Hall. Copyright © 2015 by Pearson Education, Inc.
400
CHAPTER 15
The Boulder District Attorney’s Office does not consider
any member of the Ramsey family, including John, Patsy,
or Burke Ramsey, as suspects in this case. We make this announcement now because we have recently obtained this new
scientific evidence that adds significantly to the exculpatory
value of the previous scientific evidence. We do so with full
appreciation for the other evidence in this case.
Local, national, and even international publicity has focused on the murder of JonBenét Ramsey. Many members of
the public came to believe that one or more of the Ramseys,
including her mother or her father or even her brother, were
responsible for this brutal homicide. Those suspicions were not
based on evidence that had been tested in court; rather, they
were based on evidence reported by the media.
It is the responsibility of every prosecutor to seek justice.
That responsibility includes seeking justice for people whose
reputations and lives can be damaged irreparably by the lin-M
gering specter of suspicion. In a highly publicized case, the
I
detrimental impact of publicity and suspicion on people’s lives
can be extreme. The suspicions about the Ramseys in this caseL
created an ongoing living hell for the Ramsey family and their
friends, which added to their suffering from the unexplainedE
and devastating loss of JonBenét.
S
For reasons including those discussed above, we believe
that justice dictates that the Ramseys be treated only as victims,
of this very serious crime. We will accord them all the rights
guaranteed to the victims of violent crimes under the law in
Colorado and all the respect and sympathy due from one hu-S
man being to another. To the extent that this office has added to
the distress suffered by the Ramsey family at any time or to anyH
degree, I offer my deepest apology.
A
We prefer that any tips related to this ongoing investigation
be submitted in writing or via electronic mail to BoulderDA.org,N
but they can also be submitted to our tip line at (303) 441–1636.
N
This office will make no further statements.
Counterpoint
O
N
Criminalistics: An Introduction to Forensic Science, Eleventh Edition, by Richard Saferstein. Published by Prentice Hall. Copyright © 2015 by Pearson Education, Inc.
ISBN: 978-1-323-16745-8
Last year, then–Boulder, Colorado, District Attorney Mary
Keenan Lacy, who had been “investigating” the Ramsey case
for the last few years, wrote a letter to JonBenét’s father John,1
apologizing for having believed he or his wife, the late Patsy,
or their son Burke (then nine) had anything to do with their9
daughter’s 1996 death. Lacy indicated that recent tests from
0
the Bode Laboratory of Virginia revealed that their “new methodology” of touch DNA found a match that proves an intruder9
was culpable of the slaying in which the six-year-old was moT
lested, strangled and given a fractured skull.
There has always been unmatched, unknown male DNA—S
likely from saliva—in the inside crotch of the child’s underpants.
A minute amount, too degraded to get a proper DNA profile, was
mixed with her blood when someone stuck her oh-so-slightly
with the pointed end of a broken paintbrush on the night of her
death. Because the DNA was so insignificant, it was theorized
to have come from someone coughing during the manufacturing
process, then the blood drops on top rehydrated it. If the DNA
and blood were deposited at the same time, they would have degraded at the same rate—but here the blood sample was robust.
Lacy wrote that the lab discovered that sloughed-off skin
cells on the waist area of the long johns JonBenét wore over her
underpants can be matched to the underpants’ DNA.
That was great news for people who want to believe there
was an intruder with no link to the family members. No one imagines a parent could harm a child in such a brutal and horrendous
fashion. Only problem is, adults—including parents—kill kids
all the time. While this murder is unique in its application and
renown, from an investigative point of view it’s just another homicide that has to be dissected to be understood. Anyone looking
rationally at the evidence here, and assessing it as a whole, cannot be pleased with Lacy’s letter to Ramsey or the fact that she
cleared the most credible suspects in the case. At the least it sets
a terrible precedent where other people “under the umbrella of
suspicion” in other cases will demand the same treatment if their
investigations take a long time to reach a courtroom. Just because
someone isn’t on trial, or a case has gone cold, doesn’t mean that
the right people aren’t firmly under the microscope of authorities.
Mary Lacy left office in January, 2009, and the new DA, or
any in the future, can retract her pronouncement. Frankly it will
take a brave person to go against the sea of public opinion by individuals who want to blame a bogeyman. One note of encouragement is the case has been returned to the Boulder police, who are
better equipped to investigate than the DA’s office ever was. The
case had been moved to Lacy’s predecessor when the Ramsey
family complained that the police spotlight on them was unfair.
As we all know, there’s no statute of limitations on homicide.
This doesn’t take Lacy off the hook, as I see it. Here are some
facts of the case which were ignored by her reckless decision. . . .
Touch DNA is nothing new to law enforcement, although
Bode has only tested for it for about three years. For some ten
years, the FBI lab at Quantico and other labs have used it to capture
skin cells from inside masks or gloves, and from guns or knives.
Neither Lacy nor Bode will make available their test results so independent experts can critically review the information. If scientific evidence is to be used to make an argument,
proof should be offered. Perhaps some media outlet will file a
lawsuit to compel the documents.
What Lacy and Bode have said is that the mystery man’s
DNA is on the waist area, and that the DNA doesn’t match
any Ramsey family member. Nothing is stated about where
and how much Ramsey DNA was discovered. Patsy dressed
the child in those long johns before putting her to bed, and the
waistband is precisely what John’s two hands touched when he
carried his daughter’s stiff body in a vertical position upstairs
from the basement where she was found deceased. And since
DNA can survive multiple launderings, we can’t pinpoint when
that touch DNA was left on the waistband.
Boulder County Coroner Dr. John Meyer’s autopsy report
is the Rosetta Stone to this case. It explains the type and order
of JonBenét’s injuries—asphyxiation by a ligature, then a head
blow. It does not reveal who killed the girl. Due to the three-page
phony ransom note that many analysts believe was penned by
Patsy, the working strategy was to consider Mrs. Ramsey as the
perpetrator of all the insults inflicted upon the tot. But while there
might have been enough evidence for an arrest, there was not
enough for a conviction—and among insiders there was debate
about who—if anyone in the household—did what. Without a
clear through-line that police and prosecutors could agree upon,
what chance would a jury have to find its way to a guilty verdict?
What the autopsy report states without equivocation is that
the child suffered vaginal injuries that were “chronic,” meaning they predated the murder by days or weeks. We’re talking
repeated digital penetration that eroded—not ruptured—her
DNA: THE INDISPENSABLE FORENSIC SCIENCE TOOL
hymen. Also, the opening of her vagina was twice the size of a
similar aged child’s. These factors would have been testified to
by at least three pediatric gynecological physicians, had the case
gone to trial. This unknown pedophile would have needed ongoing intimate access to JonBenét before the night she died. Mary
Lacy’s early prosecutorial career was as a sex crimes expert, so
why didn’t she recognize the nature of this little girl’s injuries?
If some accident led to JonBenét being strangled, then hit violently in the head, a normal reaction would have been for her caretakers to rush her to a hospital. But that didn’t happen, I surmise,
because her pre-existing genital injuries would have been noticed.
And so, a ridiculous—and sadly, effective—cover-up ensued.
Mary Lacy was responsible for the 2006 debacle where
she had arrested and brought back from Thailand a false confessor named John Mark Karr. When the underpants’ DNA
excluded him from being the perpetrator she let him go and
M
publicly stated: “The DNA could be an artifact. It isn’t necessarily the killer’s. There’s a probability that it’s the killer’s. But
I
it could be something else.”
She added: “No one is really cleared of a homicide until
L
there’s a conviction in court, beyond a reasonable doubt. And I
E
don’t think you will get any prosecutor, unless they were present with the person at the time of the crime, to clear someone.”
S
What made her change her thinking when she cleared the
Ramseys?
,
More to the point, where are the intruder’s skin cells from
the rope around the child’s neck, the paintbrush, the spoon and
bowl of pineapple she ate from just before she died, the white
S
blanket that covered her, the flashlight believed to have hit her
H
head, and the pen and paper used in the bogus ransom note? And
where is the intruder’s touch DNA on the waistband of JonBenét’s
A
underpants? Did the stranger pull down her long johns, then command her to pull down her own panties? Are we to believe he then
N
put on gloves—or maybe a whole scuba suit, since there were no
unidentified footprints, finger- or handprints, hairs or fibers? N
Woven inside the rope around the neck, which was
O
wrapped around a piece of a broken paintbrush, were fibers
N
401
from the distinctive jacket Patsy wore that evening—and, allegedly, inside the underpants were fibers from the wool sweater
John had on. Patsy’s fibers were also in the tote where the
paintbrush came from and on the sticky side of the piece of
duct tape that covered JonBenét’s mouth—a length of tape so
small it could have been easily flicked aside by her tongue if it
had been placed on her mouth while she was alive.
Lacy wrote that autopsy personnel were swabbed and
tested for a DNA match, and thus excluded. But what about
crime scene workers or lab technicians? And how many markers are in the touch DNA profile? The underpants’ DNA was
not enough to get a proper match through CODIS, the federal
database. That didn’t stop Lacy from sending it through on a
regular basis—such busywork has little prospect of ending with
a match, but it makes it seem as if something is being done.
Years ago, there was a civil suit in this case wherein a
federal judge issued a statement that said, based on her reading
of the material submitted to her, there was a higher likelihood
of an intruder being the killer than a family member. At that
time, Mary Lacy read a statement that suggested the Ramseys
were innocent, based on the judicial ruling—though not clearing them. That statement was reportedly dictated to her by a
Ramsey associate. What only those close to the case know is
that one side of the civil suit completely abandoned its case,
never offering paperwork, so the only information the judge
had was that which came from the Ramsey camp. Ergo, an easy
decision for the judge to make. Since then, Ramsey advisers
have pummeled Lacy to clear the family entirely and eventually it happened.
It’s egregious when an officer of the court misrepresents
scientific evidence to win political favor. Mary Lacy was right
to offer up an apology. But it should have been to JonBenét and
not her family.
Source: Dawna Kaufmann, investigative journalist. Co-author with
Cyril H. Wecht, MD, JD, of A Question of Murder, Final Exams: True
Crime cases from Cyril Wecht, and From Crime Scene to Courtroom.
1
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ISBN: 978-1-323-16745-8
chapter summary
Portions of the DNA structure are as unique to each individual
as fingerprints. The gene is the fundamental unit of heredity.
Each gene is actually composed of DNA specifically designed
to control the genetic traits of our cells. DNA is constructed
as a very large molecule made by linking a series of repeating
units called nucleotides. Four types of bases are associated
with the DNA structure: adenine (A), guanine (G), cytosine
(C), and thymine (T). The bases on each strand are properly
aligned in a double-helix configuration. As a result, adenine
pairs with thymine and guanine pairs with cytosine. This concept is known as base pairing. The order of the bases is what
distinguishes different DNA strands.
Portions of the DNA molecule contain sequences of bases
that are repeated numerous times. To a forensic scientist, these
tandem repeats offer a means of distinguishing one individual from another through DNA typing. Length differences
Criminalistics: An Introduction to Forensic Science, Eleventh Edition, by Richard Saferstein. Published by Prentice Hall. Copyright © 2015 by Pearson Education, Inc.
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CHAPTER 15
associated with relatively short repeating DNA strands are
called short tandem repeats (STRs) and form the basis for the
current DNA-typing procedure. They serve as useful markers
for identification because they are found in great abundance
throughout the human genome. STRs normally consist of
repeating sequences 3 to 7 bases long, and the entire strand
of an STR is also very short, less than 450 bases long. This
means that STRs are much less susceptible to degradation and
may often be recovered from bodies or stains that have been
subjected to decomposition. Also, because of their shortness,
STRs are ideal candidates for multiplication by PCR, in which
STR strands are multiplied over a billionfold. PCR is responsible for the ability of STR typing to detect the genetic material of as few as 18 DNA-bearing cells. The more STRs one
can characterize, the smaller the percentage of the population
from which a particular combination of STRs can emanate.
review questions
1. The fundamental unit of heredity is the ___________.
2. Each gene is actually composed of ___________, specifically designed to carry out a single body function.
3. A(n) ___________ is a very large molecule made by
linking a series of repeating units.
4. A(n) ___________ is composed of a sugar molecule, a
phosphorus-containing group, and a nitrogen-containing
molecule called a base.
5. DNA is actually a very large molecule made by linking
a series of ___________ to form a natural polymer.
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15. True or False: All of the letter sequences in DNA code
for the production of proteins. ___________
16. In STR DNA typing, a typical DNA pattern shows (two,
three) bands.
17. True or False: Specimens amenable to DNA typing are
blood, semen, body tissues, and hair. ___________
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N
N 19.
O 20.
N
21.
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22.
23.
24.
25.
Short DNA segments containing repeating sequences of
three to seven bases are called ___________.
True or False: The longer the DNA strand, the less susceptible it is to degradation. ___________
The short length of STRs allows them to be replicated by
___________.
Used as markers for identification purposes,
___________ are locations on the chromosome that contain short sequences that repeat themselves within the
DNA molecule and in great abundance throughout the
human genome.
(CODIS, AFIS) maintains local, state, and national databases of DNA profiles from convicted offenders, unsolved crime-scene evidence, and profiles of missing
people.
Amazingly, the sensitivity of STR profiling requires
only ___________ DNA-bearing cells to obtain an STR
profile.
During evidence collection, all body fluids must be
assumed to be ___________ and handled with latexgloved hands.
The concept of (CODIS, multiplexing) involves simultaneous detection of more than one DNA marker.
Criminalistics: An Introduction to Forensic Science, Eleventh Edition, by Richard Saferstein. Published by Prentice Hall. Copyright © 2015 by Pearson Education, Inc.
ISBN: 978-1-323-16745-8
6. ___________ different bases are associated with the
makeup of DNA.
7. Watson and Crick demonstrated that DNA is composed
of two strands coiled into the shape of a(n) ___________.
8. The structure of DNA requires the pairing of base A to
___________ and base G to ___________.
9. The base sequence T–G–C–A can be paired with the base
sequence ___________ in a double-helix configuration.
10. The inheritable traits that are controlled by DNA
arise out of DNA’s ability to direct the production of
___________.
11. ___________ are derived from a combination of up to
20 known amino acids.
12. The production of an amino acid is controlled by a sequence of ___________ bases on the DNA molecule.
13. True or False: Enzymes known as DNA polymerase assemble new DNA strands into a proper base sequence
during replication. ___________
14. True or False: DNA can be copied outside a living cell.
___________
This gives rise to the concept of multiplexing. Using the technology of PCR, one can simultaneously extract and amplify a
combination of different STRs. Currently, U.S. crime laboratories have standardized on 13 STRs. With STR analysis, as
few as 125 picograms of DNA are required.
Another type of DNA used for individual characterization
is mitochondrial DNA. Mitochondrial DNA is located outside
the cell’s nucleus and is inherited from the mother. However,
mitochondrial DNA typing does not approach STR analysis in
its discrimination power and thus is best reserved for samples,
such as hair, for which STR analysis may not be possible.
Bloodstained evidence should not be packaged in plastic or airtight containers because accumulation of residual
moisture could contribute to the growth of blood-destroying
and fungi. Each stained article should be packaged
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separately in a paper bag or in a well-ventilated box.
DNA: THE INDISPENSABLE FORENSIC SCIENCE TOOL
26. The amelogenin gene shows two bands for a (male, female) and one band for a (male, female).
27. Y-STR typing is useful when one is confronted with a
DNA mixture containing more than one (male, female)
contributor.
31. True or False: Y-STR data is normally entered into the
CODIS database collection. ___________.
32. Small amounts of blood are best submitted to a crime
laboratory in a (wet, dry) condition.
33. True or False: Airtight packages make the best containers for blood-containing evidence. ___________
28. Mitochondrial DNA is inherited from the (mother,
father).
29. True or False: Mitochondrial DNA is more plentiful in
the human cell than is nuclear DNA. ___________
34. Whole blood collected for DNA-typing purposes must
be placed in a vacuum containing the preservative
___________.
35. A typical STR DNA type emanating from a single individual shows a (one, two, three)-band pattern.
30. The national DNA database in the United States has
standardized on ___________ STRs for entry into the
database.
review questions for inside
1. True or False: Enzymes known as DNA polymerases
assemble new DNA strands into a proper base sequence based off the template strand during replication.
___________
2. DNA evidence at a crime scene can be copied by the
processes of the ___________ with the aid of a DNA
polymerase and specific primers.
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science
DNA fragments can be separated and iden…