Practice Genetics Problems
1) The "R" allele is a dominant allele specifying for round seeds (in peas), while the "r" allele is the recessive allele
specifying for wrinkled seeds. Use Punnett squares to determine the offspring genotypes and phenotypes (and their
frequencies) from the following crosses:
a. Rr x Rr
b. Rr x rr
c. RR x Rr
2) A brown mink crossed with a silver mink produced all brown offspring. When these F1 minks were crossed among
themselves they produced 47 brown animals and 15 silver animals (F2 generation).
a. Based on these F2 phenotypes, determine the most likely genotypes for the original parents and the F1 minks.
b. What are the genotype ratios of the F2 minks?
3) The "Y" allele specifies for the dominant yellow seed color trait, while "y" specifies for green seeds (recessive).
Use Punnett squares to determine the offspring genotypes and phenotypes (and their frequencies) from the
following crosses (assume independent assortment):
a. RrYy x RrYy
b. RrYy x rryy
4) In turkeys, a dominant gene B produces the familiar bronze color; its recessive allele b results in red. Another
dominant gene F results in normal feathers; its recessive allele f produces feathers without webbing, so that they
resemble tufts of hair. Two bronze turkeys with normal feathers were mated, and their offspring consisted of 8
bronze with normal feathers, three bronze with hairy feathers, two red with normal feathers, and one red with hairy
feathers. What were the genotypes of the parents?
5) 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 allele T, and the 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 F1 generation?
6) Assume right-handedness (R) dominates over left-handedness (r) in humans, and that brown eyes (B) are dominant
over blue (b). A right-handed, blue-eyed man marries a right-handed, brown-eyed woman. One of their two children
is right-handed/blue-eyed, while the other is left-handed/brown-eyed. The man marries again, and this time the
woman is right-handed and brown-eyed. They have 10 children, all right-handed and brown-eyed. What are the
genotypes of the husband and two wives?
7) Yellow guinea pigs crossed with white ones always produce cream colored offspring. Two cream colored guinea pigs
when crossed produced yellow, cream, and white offspring in the ratio of 4 yellow: 9 cream: 5 white. How are these
colors inherited? Use a Punnett square to show how this mode of inheritance can produce the observed results.
8) In humans the blood groups are produced by various combinations of three alleles IA, IB, and i. Blood type A is
caused by either IA IA or IA i; type B by IB IB or IB i; type AB by IA IB; and type O by i i.
Suppose a child is of blood type A and the mother is of type O. What type or types may the father belong to?
9) Suppose a father of blood type B and a mother of blood type O have a child of type O. What are the chances that
their next child will be blood type O? Type B? Type A? Type AB?
10) A new father and mother claim they have been given the wrong baby at the hospital because they are blood type A,
and the baby is blood type O. What would you tell them?