Punnett Squares

Week 7 Assignment: Punnett Squares
Exercise 1: Monohybrid Crosses
Complete the following Punnett squares and answer the following questions:
1. Cross two pea plants: one is homozygous for a dominant trait, yellow
pods, the other is homozygous for a recessive trait, green pods.
2. What are the possible genotypes of the offspring in the cross above
and what percentage of the offspring have each genotype?
3. What are the possible phenotypes of the offspring in the cross above
and what percentage of the offspring have each phenotype?
Exercise 2: Codominance
SCI1015
College of Online Education
Johnson & Wales University
When codominance occurs, two non-identical alleles of a gene are both fully
expressed in heterozygotes. A good example of codominance is ABO blood
types.
4. First, determine the possible genotypes of each blood type. (HINT:
some may have two possibilities.)
Phenotype (Blood Type)
Possible Genotype
A
B
AB
O
8. Using the Punnet square below, show the cross between a man with
AB blood and a woman with O blood.
9. What are the possible blood types their children could have and at
what ratios?
Exercise 3: Autosomal Dominant and Recessive Traits
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College of Online Education
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Most genes are carried on the 22 chromosomes that are not the sex
chromosomes X and Y. These are called autosomes, and traits with genes
found on these chromosomes are called autosomal traits.
Autosomal Dominance – Achondroplasia
10.
First, determine the possible genotypes of each of the following:
Phenotype (Disorder Status)
Genotypes
Person with Achondroplasia
Person without Achondroplasia
13.
Using the Punnett square below, show how it is possible for two
people who have achondroplasia to have a child that does not have
achondroplasia.
14.
What are the chances of a couple who both have achondroplasia
to have a child without achondroplasia?
SCI1015
College of Online Education
Johnson & Wales University
Autosomal Recessive Traits – Tay-Sachs Disease
15.
First, determine the possible genotypes of each of the following:
Phenotype (Disorder Status)
Genotype
Person with Tay-Sachs
Person without Tay-Sachs (non-carrier)
Carrier of Tay-Sachs
16.
Using the Punnett square below, please show a cross between
two carriers of Tay-Sachs disease.
17.
What are the chances of a couple who are both carriers to have
a child who does not have Tay-Sachs disease?
SCI1015
College of Online Education
Johnson & Wales University
Exercise 4: X-Linked Inheritance
X-linked Inheritance
Some genes are carried on the sex chromosomes X and Y, and are therefore
passed along based on what sex the offspring turn out to be. Colorblindness
is a good example of a disorder caused by a gene carried on the X
chromosome.
18.
First, determine the possible genotypes of each of the following:
Phenotype (Colorblind Status)
Genotype
Colorblind Male
Normal Male
Colorblind Female
Normal Female (non-carrier)
Carrier Female
19.
Using the Punnet square below, show the cross between a
colorblind male and a normal female (non-carrier).
20.
What are the chances that they would have a colorblind son?
SCI1015
College of Online Education
Johnson & Wales University
21.
Using the Punnet square below, show the cross between a
colorblind male and a carrier female.
22.
What are the chances that they would have a colorblind son?
23.
What are the chances that they would have a colorblind
daughter?
24.
What are the chances that they would have a daughter that is
not colorblind, but is a carrier for colorblindness?
SCI1015
College of Online Education
Johnson & Wales University