Description
GENETICS PROBLEMS
In this homework exercise you are expected to show your work for problems 3, 6-14, 16, and 17. Place your
work and answers in order on a separate sheet(s) of paper. Circle the final answer(s) for each numbered
question. This is a twenty point exercise. Don’t fail to turn it in, whatever your progress.
1. What are the alleles for a person with the genotype of AO using the ABO blood type system?
2. Next, consider a gene with the alleles of A & a. If each person has two alleles, one from each parent,
what are the three possible combinations these alleles could form in individuals?
3. From question two you identified three different genotypes possible for a gene with the alleles A & a.
These three types of genotypes can be crossed in six different matches. Write out the possible
breeding crosses and give the results of each of the crosses in the form of genotypic and phenotypic
ratios.
1.
2.
3.
4.
5.
6.
Genotype 1 X genotype 2 = genotypic ratio & phenotypic ratio
List the crosses below
List the genotypic ratio
List the phenotypic ratio
AA X AA
1AA : 0
1A_ : 0
Note there are only six basic crosses and four different ratios that are fundamental to all Mendelian ratios.
4. Consider two different genes, one with the alleles A & a and the other with the alleles of B & b. From
the genotypes of these individuals, a-d, determine the possible allelic combinations that could be
formed in their gametes (sperm & egg cells).
a) AABB
b) AaBB
c) AaBb
d) Aabb
5. A spotted rabbit when crossed with a solid colored rabbit produced all spotted offspring. When these F1
generation rabbits were crossed among themselves, they produced 32 spotted and 10 solid colored rabbits.
Which of these characteristics is likely due to a dominant gene?
6. How many of the spotted rabbits in all the F2 generation of the preceding problem (#5) would be expected to
be homozygous? How many of the solid colored F2 generation rabbits would be homozygous.
7. If you were physically examining the spotted rabbits in the F2 generation of problem number six how could
you tell which were homozygous and which were heterozygous? In the next step explain how you would go
about finding this information out. (Hint! What type of experimental crosses would you perform? Do not
explain how you got the answer in question #6))
8. In a flower called Japanese Four-o’clocks when red flowers are crossed with white ones they always
produce pink colored flowers (an example of incomplete dominance). Two pink colored flowers when
crossed produced red, pink and white offspring in a ratio of 1 red: 2 pink: 1 white. Show by Punnet squares
how these colors are inherited (remember to diagram both crosses).
9. In horses, black is dependent upon a dominant gene B and chestnut upon its recessive allele b. The trotting
gait is due to a dominant gene T, and pacing gait to its recessive allele t. If a homozygous black pacer is
mated to a homozygous chestnut trotter, what will be the appearance of the individuals in the F1 generation?
10. If two individuals from the F1 generation in the preceding problem are mated, what kinds of offspring could
they have, and in what proportions. Provide both the genotypic and phenotypic ratios. (3 points)
11. Aniridia is a type of blindness due to a single dominant gene. Migraine headache is the result of a different
dominant gene. A man with aniridia, but normal headaches whose mother was not blind, marries a woman
who suffers from migraines and has normal vision but whose father did not have migraine headaches. What
is the expected proportion of their children that would have both aniridia and migraines together?
12. Tyrosinase-negative oculocutaneous albinism (“T” albinism) is caused by an autosomal recessive gene. A
man displaying “T” albinism marries a woman with normal skin pigmentation and they have ten children,
and they all have normal skin pigmentation. What are the genotypes of all of the individuals in the family?
13. A tongue rolling man marries a woman who cannot roll her tongue. Their first child is a non-roller. If
another child is born to this couple, what chances are there for both the rolling and non-rolling trait
considering the second cross alone?
14. Woody Guthrie was a folk singer that was diagnosed with a genetic disorder called Huntington’s disease. A
dominant autosomal gene causes Huntington’s disease. If Woody Guthrie was heterozygous for this gene,
then what are the chances his children will have the disorder. Assume his wife is homozygous normal for
this condition.
15. Recall that human sex chromosomes are XX for females and XY for males.
a.
b.
c.
Does a male child inherit his X chromosome from his mother or father?
If a female is homozygous for an X-linked gene, how many different types of gametes can she
produce with respect to this gene?
If a female if heterozygous for an X-linked gene, how many different types of gametes can she
produce with respect to this gene?
16. Hemophilia is inherited as an X-linked recessive. A woman has a brother with this defect and a mother and
father who are phenotypically normal. What is the probability that this woman will be a carrier if she herself
is phenotypically normal?
17. Red-green color blindness is due to a recessive allele inherited on the X chromosome. In the following
mating, give the probability that the son will have the defect. (2 points)
a.
b.
c.
d.
Carrier female X normal male
Carrier female X color-blind male
Color-blind female X normal male
Could any of the above matings produce a color-blind daughter?
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