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Genetics Problem Set Review
1. From the following individuals, what are the possible gametes that can be produced?
a)
b)
c)
d)
Tt
gg
WW
ss
2. Two black guinea pigs were mated and over several years produced 29 black and 9
white offspring. Explain these results, giving the genotypes of parents and progeny.
3. Huntington’s chorea is a rare fatal disease that usually develops in middle age. It is
caused by a dominant allele. A phenotypically normal man in his early twenties learns
that his father has developed Huntington’s chorea. What is the probability that he himself
will develop the symptoms later on (assume the man’s mother does not carry the gene)?
4. Holstein cattle normally are black and white. A superb black and white bull, Charlie,
was purchased by a farmer for $100,000. The progeny sired by Charlie were all normal in
appearance. However, certain pairs of his progeny, when inbred, produced red and white
progeny at a frequency of about 25%. Charlie was soon removed from the stud list of
Holstein breeders. Explain precisely why, using symbols. The cows Charlie was bred to
were known to be purebred black and whites.
5. Suppose that a husband and wife are both heterozygous for a recessive gene for
albinism. If they have dizygotic twins (two-egg, a.k.a fraternal twins) , what is the
probability that both of the twins will have the same phenotype with respect to
pigmentation.
6. Polydactyly, or six fingers and/or six toes, is controlled by a single gene displaying
simple dominance (polydactyly is dominant). Suppose a woman heterozygous for
polydactyly mates with a normal man. What are the chances that their children will have
six fingers and/or toes?
7. Tay-Sachs is a human genetic disorder resulting in fatal brain damage. It mainly
affects infants of East European Jewish ancestry. Homozygous recessive children are
affected. Parents who do not have Tay-Sachs produce a child who has the disease. What
are the chances that each child born to this couple will have Tay-Sachs?
8. Sickle cell anemia (SCA) is a human genetic disorder caused by a recessive allele. A
couple plan to marry and want to know the probability that they will have an affected
child. With your knowledge of Mendelian inheritance, what can you tell them if (a) both
are normal, but each has one affected parent and the other parent has no family history of
SCA; and (b) the man is affected by the disorder, but the woman has no family history of
SCA.