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UMUC Asia DE lab – Evolution
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Lab 8. Evolution
Introduction
Evolution is often defined as change over time, usually in response to a change in the environment. What this means is that the gene pool of a population shifts as time passes.
What is a gene pool? It is simply the collection of all the available alleles of all the genes on all the chromosomes in the population. What’s a population? It is the group of individuals that have geographic and behavioral mating access to each other. Geographic access is obvious; the dandelions in a yard in Virginia are not in the same gene pool as those in a yard in Pennsylvania, even if they are the same species. They could mate if they were brought together, but dandelion pollen doesn’t blow that far, so they are geographically isolated. Behavioral mating access can be less obvious; one example would be a stag that keeps all other males out of his territory and mates with all the does. The other stags are not allowed to mate, so their genes are not in the pool.
A great deal of the time for most species, evolution is not occurring. The gene pool stays the same, because the environmental situation is not changing. In the early days of population genetics, people argued over whether dominant alleles could “take over” a gene pool without any selection. Two mathematicians, Hardy and Weinberg, showed that this would not happen.
The basis of their argument is that the gene pool will not change, and the frequency of the various alleles will stay the same if the following conditions are met:
· The population is large.
· The population is freely interbreeding at random (this excludes the stag and the does).
· No individuals are taking their alleles out of the population (emigrating) or adding their alleles to the population (immigrating), so the percentages of the alleles can’t change because of migration.
· There are no mutations, so no new alleles appear.
· None of the alleles has a selective advantage (in other words, there aren’t any combinations of alleles that give some individuals a better chance of surviving that anyone else).
Here is the mathematical basis of their argument:
Imagine a simple situation in which a gene has only two alleles, A and a, and A is dominant. Let the frequency of A, expressed as a decimal with a value less than one, be p, and let the frequency of a, expressed as a decimal with a value less than one, be q. Because there are only two alleles, every allele must be either A or a, so,
p + q = 1
By definition,
p
and
q
are also the frequencies of the alleles in the eggs and sperm produced by this species. These sperm and eggs can come together in four ways when random mating occurs.
1. The chance that a male p sperm will meet a female p egg is p x p, or p2. The children produced by this cross will be genetically AA and express the dominant allele; they will have the A phenotype.
2. The chance that a male p sperm will meet a female q egg is p x q, or pq. The children produced by this cross will be genetically Aa and express the dominant allele; they will also have the A phenotype.
3. The chance that a male q sperm will meet a female p egg is also p x q, or pq. The children produced by this cross will also be genetically Aa and express the dominant allele; they will also have the A phenotype.
4. The chance that a male q sperm will meet a female q egg is q
x
q, or q2. The children produced by this cross will be genetically aa and express the recessive allele; they will have the a phenotype.
These four situations are the only possibilities, so
p2 + pq + pq + q2 = 1 (1.0 represents 100% of all possible events in a mating)
When we combine the middle two terms, we get
p2 + 2pq + q2 = 1
These two formulas,
p + q = 1
p2 + 2pq + q2 = 1
summarize what is known as the Hardy-Weinberg Law.
However, usually we don’t know the frequency of the alleles in a population; in most cases, we can’t even see the gametes! If we want to know what the frequencies of the alleles are, we have to use these two formulas to figure it out.
The most important things to remember are the two formulas above. In these formulas,
· p = the frequency of the dominant allele
· q = the frequency of the recessive allele
· p2 = the frequency of individuals in the population who are homozygous dominant
· 2pq = the frequency of individuals in the population who are heterozygous
· q2 = the frequency of individuals in the population who are homozygous recessive
Materials
· Three colours of beans (chili, pinto and navy are good, but any three contrasting objects will do – M&Ms, coins, beads, etc).
· Two bowls
· A pocket calculator (MS Windows has one too)
Procedure
Two alleles which control hair texture are incompletely dominant to each other, and the phenotypic expression of hair texture is a function of which alleles are present. The genotypes and phenotypes are:
|
Genotype |
Phenotype |
||||||||||||||
|
C1C1 |
curly |
||||||||||||||
|
C1C2 |
wavy |
||||||||||||||
|
C2C2 |
straight |
This is where Hardy-Weinberg comes in. Recall:
p2 + 2pq + q2 = 1.0
Remember:
p2 = the frequency of the C1C1s
2pq = the frequency of the C1C2s
q2 = the frequency of the C2C2s
These percentages will remain stable through all subsequent rounds of mating of this population.
Please refer to the following table for calculation references. Also, please adjust the calculations for the rest of the tables.
Please submit this Lab Report Sheet in Webtycho in the Assignments folder.
Data Sheet – Sample table and calculations:
Student answers to questions
1. In the absence of selection, what happens to gene frequencies in a population?
Type your answer here. This textbox expands as you type.
2. What have you learned about population genetics so far? i.e., what do these results tell you about how genes in a gene pool behave under tightly controlled (i.e., artificial/hypothetical) circumstances?
Type your answer here. This textbox expands as you type.
You’ll use your three colours of beans (or any 3 objects of your choice), from this point on, to represent the individuals in your population.
The red (chili) beans represent the homozygous dominants (C1C1 – curlies), the mottled (pinto) beans the heterozygotes (C1C2 – wavies), and the white (navy) beans the homozygous recessives (C2C2 – straights).
Pick the beans (objects) two at a time and record your results here. Use the example above (page 6) to help you in your calculations).
Experiment 1
In this first exercise, you are going to determine what happens when you allow your population of 80 to interbreed freely.
In a bowl, place the correct numbers of the three colours of beans to represent the population of 80 people. For 20 C1C1s, 40 C1C2‘s, and 20 C2C2’s, you would choose 20 red beans, 40 pinto beans, and 20 white beans (or any three different objects you chose). Mix them thoroughly and then, without peeking (i.e., at random), withdraw two beans (or two objects). Record the genotypes represented by the two beans.
Example
: if you withdraw a white bean and a pinto bean the first time, then you will record one (1) C2C2 x C1C2; you have mated one pair.
Put your first two beans in the second bowl and continue to draw pairs of beans from the first bowl until you have withdrawn all 40 pairs. Your records will now show a series of 80 random matings from this population.
There are six possible combinations:
1. C1C1 x C1C1 (two chili beans),
2. C1C1 x C1C2 (one chili, one pinto),
3. C1C1 x C2C2 (one chili, one navy),
4. C1C2 x C1C2 (two pintos),
5. C1C2 x C2C2 (one pinto, one navy), and
6. C2C2 x C2C2 (two navies).
Record the
total
number for each of the six matings.
Data sheet (fill in the BLUE and YELLOW areas).
(see page 6 for detailed calculation help).
|
MATINGS |
OFFSPRING = Matings x 4 |
C1S |
C2S |
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
X |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| total |
|
P= |
Frequency of C1 = |
||||||
|
Q= |
Frequency of C2 = |
3. How do these compare with the parental generation?
Type your answer here. This textbox expands as you type.
4. What principle have you demonstrated with this exercise?
Type your answer here. This textbox expands as you type.
Experiment 2
Put your beans back in the bowl. This time,
withdraw only 20 pairs
(= 20 random matings), and record the results as you did in Task 1.
Next, calculate the offspring of this generation: again, assume 4 offspring per mating. Total the numbers of C1C1s, C1C2s and C2C2s. and then calculate the allele frequencies. Finally, determine the genotypic frequencies.
Data sheet (fill in the BLUE and YELLOW areas).
(see page 6 for detailed calculation help).
MATINGS
OFFSPRING = Matings x 4
C1S
C2S
C1C1
X
C1C1
C1C1
X
C1C2
C1C1
X
C2C2
C1C2
X
C1C2
C1C2
X
C2C2
C2C2
X
C2C2
total
P=
Frequency of C1 =
Q=
Frequency of C2 =
5. How do these last P and Q (frequencies) compare with the P (parental) generation (Experiment 1)?
Type your answer here. This textbox expands as you type.
6. If you repeated this experiment (i.e., you selected another 20 pairs from the bowl) would you expect to get the same result? Why or why not?
Type your answer here. This textbox expands as you type.
7. What principle have you illustrated this time?
Type your answer here. This textbox expands as you type.
Experiment 3
Now you are going to assume that your population has been invaded by an ET which is a human predator. It particularly fancies people with curly hair – eats them preferentially – and when it moves on (looking for more of its favourite lunch), your population has been denuded of curlies (C1C1).
Set up your new population in the bowl, and go through the mating (bean picking/ withdrawal) procedure again, recording your results. Again, assume that each mating produces four offspring.
(see page 6 for detailed calculation help).
P=
Frequency of C1 =
Q=
Frequency of C2 =
8. What is going on?
Type your answer here. This textbox expands as you type.
9. How have the relative proportions of C1s and C2s changed?
Type your answer here. This textbox expands as you type.
10. What principle have you demonstrated here?
Type your answer here. This textbox expands as you type.
Experiment 4
Go back to your population in Experiment 3. This time, assume that through some further natural disaster which has discriminated against people with wavy hair,
half the wavies
have also been lost. Allow this population to breed at random and determine the outcome of the next generation.
(see page 6 for detailed calculation help).
MATINGS
OFFSPRING = Matings x 4
C1S
C2S
C1C2
X
C1C2
C1C2
X
C2C2
C2C2
X
C2C2
total
P=
Frequency of C1 =
Q=
Frequency of C2 =
13. What is going on this time?
Type your answer here. This textbox expands as you type.
14. What if this trend continues?
Type your answer here. This textbox expands as you type.
SUMMARY
15. Summarize what you have learned from this lab about the principles of evolution.
Type your answer here. This textbox expands as you type.
Define (one short sentence each):
1) Evolution
2) Microevolution
3) Macroevolution
4) Genetic Drift
5) Natural selection
What did you learn about or in each of the following?
a) The Hardy-Weinberg Equilibrium
b) Experiment 1
c) Experiment 2
d) Experiment 3
e) Experiment 4
PAGE
Page 2 of 15
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iol
10
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© UMU
C
.
A
ll rights reserved.
Classification lab
Biol 102, UMUC
Classification lab
>Overview
Taxonomy is the study of the classification of organisms. Classification is simply a way of sorting things in an orderly manner.
F
or example, if you have a box of mixed stationary supplies on your desk—paper clips, staples, rubber bands, and thumb tacks—and you decide to put them into four separate containers so that you can use them more efficiently, you are classifying them.
There are at least two million species of organisms alive on the planet right now, most of them insects. There have been many other species that are now extinct. To try to keep them in some kind of order to examine, compare, and discuss them in a consistent manner, biologists have set up a system known as the binomial system of nomenclature.
I
n this system, two names are assigned to each organism, a genus name and a species name. The genus name indicates the group of related species to which the organism belongs, and the species name indicates the specific species.
For example, the scientific name for a chimpanzee is Pan troglodytes. Pan is the genus name, and troglodytes is the species name. By convention, both words are written in italics or underlined. Note that the more general term comes first. If the American president Abraham
L
incoln had been a species all by himself, his name would have been Lincoln abraham.
Starr (2000, glossary) defines a species as “one kind of organism.” Among sexually reproducing organisms, a species is a group of naturally interbreeding organisms that form a genetically distinctive population reproductively isolated from all others. Your textbook provides greater detail on the technical definition of a species.
A group of closely related species forms a genus. The plural of genus is genera.
G
enera are grouped into families, families into orders, orders into classes, classes into phyla (the single is phylum), and phyla into kingdoms. These levels are grouped based on their common characteristics. Your textbook discusses some of these defining characteristics in some detail.
The value of this system is that it not only gives each species a name, but that it also puts it in a series of categories that indicate its relationship to other similar species and also to more distantly related ones.
Let’s go back to the chimpanzee. Pan troglodytes belongs to the family Pongidae, which includes the gorillas and the orangutans. They all have distinctive molar teeth; flexible arm and shoulder joints; arms longer than legs; and large complex brains. None of them have a tail. The Pongidae belong to the order Primata, which includes, in addition to the Pongidae, all the monkeys and the prosimians, such as lemurs. All of these animals are grouped together because they share a large group of behavioral and anatomical characteristics. These include excellent manual dexterity, a well-developed sense of sight, a dependence upon learned behavior, a long infant-dependency period, a complex social organization, prehensile hands with opposable thumbs, mobile arms, binocular vision, and a reduced snout.
The primates belong to the class Mammalia, which are animals with hair or fur, high and controlled body temperature, glands that produce milk, and complex teeth. The mammals belong to the phylum Chordata, all of which have, at some stage in their development, a dorsal stiffening rod (notochord) as the chief internal support, a tubular nerve cord above the notochord, gill slits leading into the anterior part of the digestive tract, and a post-anal tail. In a chimpanzee, most of these disappear during embryonic development, but they are all there at some stage.
Finally, the chordates belong to the kingdom Animalia. All animals are multicellular heterotrophs that usually ingest food and digest it in an internal cavity. Their cells lack the rigid cell walls that characterize plant cells. Most animals are capable of complex and relatively rapid movement and most reproduce sexually.
As you can see, a taxonomic system goes from very specific characteristics to very general ones. This information can be used to create a dichotomous classification key, which is very simply a system for identifying organisms in the field. At each step, you are given two choices for a given characteristic; these lead you to further choices more specifically identifying the species until you finally have its name (or if you’re really lucky, a discovery of a new species).
Lab Activities
>A. Using a
D
ichotomous
K
ey
Lab Materials
Materials in your lab kit:
· none needed
Being able to use a dichotomous key is a very useful skill. Many field guides, particularly ones that help you to identify plants, are based on this principle. In this activity, you will use a classification key to determine the names of nine species of fish. To do so, you begin with the first pair of choices on the key, working your way downward until you’ve successfully identified the fish.
1. Review the following definitions and key to get a feel for what you will be looking for in identifying the fish.
Definitions
dorsaltoward the backbone side of the fish
ventraltoward the belly side of the fish
caudaltoward the tail end of the fish
pharynxthe throat region of the fish behind the head
pectoral finthe fin on the side of the fish nearer the head
pelvic finthe fin on the side of the fish nearer the tail
Simple Classification Key for Some Pacific Fishes
|
Choice |
Characteristic |
Next Move or Identification |
|||
|
1a |
Fish has 5 or 6 gill openings on each side of the pharynx |
2 | |||
|
1b |
Fish has only one covered gill opening on each side of its pharynx |
3 | |||
|
2a |
Very large, stout bodied; caudal fin is crescent shaped and nearly symmetrical |
White shark |
|||
|
2b |
Large, slender bodied; dorsal lobe of caudal fin is much longer than the ventral lobe |
Blue shark |
|||
|
3a |
One eye on each side of the head |
4 | |||
|
3b |
Both eyes on one side of the head |
Flathead sole |
|||
|
4a |
Pectoral fins and pelvic fins present |
5 | |||
|
4b |
Pectoral and pelvic fins absent |
Moray eel |
|||
|
5a |
One dorsal fin |
6 | |||
|
5b |
More than one dorsal fin |
7 |
|||
|
6a |
Long winglike pectoral fin |
California flying fish |
|||
|
6b |
Small pectoral fin low on side |
8 |
|||
|
7a |
2 dorsal fins |
Great sculpin |
|||
|
7b |
3 dorsal fins |
Pacific cod |
|||
|
8a |
Large black oval spots over all of upper body and caudal fin |
Pink salmon |
|||
|
8b |
Fine specks on back, but no black spots |
Chum salmon |
2. Using the key above, identify the following fish and type the name of each fish next to its letter:
(type your answers in the BOX
E
S below each fish):
|
A |
B |
C |
|
D |
E |
F |
|
G |
H |
I |
(Fish drawings copyright by Houghton Mifflin and Eschmeyer & Herald)
References
Eschmeyer, W. N., and E. S. Herald. (1983). The Peterson field guide series: A field guide to Pacific coast fishes—North America. New York: Houghton Mifflin. (Plates 2, 6, 8, 11, 12, 16, 45)
Gendron, Robert P., Ph.D. (2000). “Classification and evolution.” Indiana University of Pennsylvania Biology Department. Retrieved April 18, 2002, from
http://nsm1.nsm.iup.edu/rgendron/camin.htmlx
.
Starr, Cecie. (2000). Basic concepts in biology. 4th ed. Stamford: Thompson.
B. Taxonomic Classification
Materials in your lab kit:
· none
Additional materials you will need:
· scissors (optional)
(The following exercise was modified from one designed by Robert P. Gendron, Ph.D., of Indiana University of Pennsylvania. His permission to use it is gratefully acknowledged.)
In order to design a dichotomous key for a group of related organisms, you must first examine your specimens and determine their specific characteristics. Then you must use these characteristics to categorize them into larger and larger groups such as genera, families, orders, and classes. In the overview for this lab, you were given the description of the classification of the chimpanzee as an example. For this exercise, you are going to design a dichotomous key to sort fourteen living species of caminalcules, which are imaginary animals invented by the evolutionary biologist,
J
oseph Camin. These animals are pictured below:
Living Caminalcules
(Caminalcule pictures copyright by Systematic Biology and Robert R. Sokal.)
Supersize me version (
Print this out and cut out each one to help you rearrange and re-examine them.
Each caminalcule has a number designation as its common name. You may consider these drawings to be life size. Examine the pictures and note the variety of
appendages, shell shape, color pattern, size, and any other details
that you notice. You may find it easier to do this if you print the page, cut out the creatures, and move them around on your physical desktop.
Now create a hierarchical classification of these species, using the format in the table below. Instead of using letters (A, B, etc.), as in this example, use the number of each caminalcule species. Keep in mind that the classification scheme below is just a hypothetical example. Your
classification may look quite different from this one.
Sample
Classification Scheme
|
Phylum Caminalcula |
|||||||||||
|
Class 1 |
Class 2 |
||||||||||
|
Order 1 |
Order 2 |
Order 3 |
|||||||||
|
Family 1 |
Family 2 |
Family 3 |
|||||||||
|
Genus 1 |
Genus 2 |
Genus 3 |
Genus 4 |
Genus 5 |
Genus 6 |
||||||
| A | G | H | D | B | J | L | E | K | C | F | I |
1. The first step in this exercise is to decide which species belong in the same genus. Species within the same genus share characteristics not found in any other genera. The caminalcules numbered 19 and 20 are a good example; they are clearly more similar to each other than either is to any of the other living species here, so we would put them together in their own genus. Use the same procedure to combine the genera into families. Again, the different genera within a family should be more similar to each other than they are to genera in other families. Families can then be combined into orders, orders into classes and so on. Depending on how you organize the species, you may only get up to the level of order or class. You do not necessarily have to get up to the level of kingdom or phylum.
One of your problems will be convergent evolution; this is a real problem faced by taxonomists every day. Look up convergent evolution in your textbook or some other reference to learn the meaning of the term.
2. Define this term in your own words and explain why it may cause you problems in this exercise. (Here is a hint: claws have arisen independently in caminalcules more than once during evolution.)
Type in here – this expands as you type.
Definition: Convergent evolution + why it may cause problems in taxonomy
3. Enter your
classification scheme
here. It does not have to be as elegant as the sample scheme above, but it does have to be clear. If you are uncertain how best to input your classification scheme, contact your instructor.
Type in here – this expands as you type.
Classification Scheme:
4. Use your classification scheme to design a
dichotomous key
that will account for the fourteen species. Remember that in each step you can only have two choices. One problem you may have is that your steps will have numbers and so do your species. To keep things clear, refer to the names of the species by using the number with the # symbol in front of it. In other words, the fourteen species names will be #1, #2, #3, #4, #9, #12, #13, #14, #16, #19, #20, #22, #24, and #26.
a. Enter your dichotomous key here. If you are uncertain how best to input your dichotomous key, contact your instructor.
Note: Table headings are as follows (see pp 3-4):
Type in here – this expands as you type.
References
Eschmeyer, W. N., and E. S. Herald. (1983). The Peterson field guide series: A field guide to Pacific coast fishes—North America. New York: Houghton Mifflin. (Plates 2, 6, 8, 11, 12, 16, 45)
Gendron, Robert P., Ph.D. (2000). “Classification and evolution.” Indiana University of Pennsylvania Biology Department. Retrieved April 18, 2002, from
http://nsm1.nsm.iup.edu/rgendron/camin.htmlx
.
Starr, Cecie. (2000). Basic concepts in biology. 4th ed. Stamford: Thompson.
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