Genetics Practice Problems
and Answers

1. In rabbits, mono-colored fur (F) is dominant over spotted fur (f), and straight ears (S) is dominant over floppy (s).

A. Your son is entering the 4-H county fair for rabbits. He has a male white rabbit without spots and crosses it with a female white rabbit without spots. Some of the baby rabbits have spots. What are the genotypes of the male and female rabbits, and the baby rabbits with spots? How did you know?

B. Complete a Punnett square for the cross above. What is the proportion of the offspring which are:
Homozygous dominant?
Homozygous recessive?
Heterozygous?
What are the expected genotypes and their ratio?
Phenotype ratio?


2. Your son is interested in obtaining a spotted floppy-eared rabbit for entry into the fair. You have a male FfSs and a female ffss, and female rabbits often produce about eight babies per litter. Figure out the ratio of poffspring for each phenotype you can expect from crossing these rabbits, so you can decide if it is likely that your son can enter the fair with a spotted floppy-eared rabbit.

A. Ratio of the offspring with:
Monocolored fur and straight ears: _____________
Monocolored fur and floppy ears: _____________
Spotted fur and straight ears: _____________
Spotted fur and floppy ears: _____________

B. A male rabbit is mated to a whole flock of spotted floppy-eared rabbits. The number of individuals and their phenotypes produced were: 30 monocolored straight-eared rabbits; 27 monocolored floppy-eared rabbits; 29 spotted straight-eared rabbits; and 31 spotted floppy-eared rabbits. Using what you know about the genotype of the mothers, decide what the genotype of the father is.


3. The ruffed chicken has an under-chin wattle. A smooth wattle (S) is dominant over a wrinkled wattle (s). A red wattle (HR) is incompletely dominant with a white wattle (HW) so that an individual with HRHW will have a pink wattle.

A. A chicken with a wrinkled red wattle is mated to a homozygous chicken with a smooth white wattle. What is the genotype and phenotype of the chicks?


4. In turkeys, bronze body color (B) is dominant over red (b). Normal feathers (N) are dominant over hairy feathers (n). A bronze male turkey is mated to a bronze female, and some of the poults (baby turkeys) produced by this cross are red. What are the genotypes of the male and female parents and the red poults?

5. Some of the poults from the cross described in #1 above are bronze. What proportion of the poults would you expect to have the BB genotype? What proportion would have the Bb genotype? What proportion would have the bb genotype?

6. If you were to cross a Bbnn turkey with a bbNn turkey, what proportion of the offspring will have red, normal feathers? What proportion will have bronze hairy feathers? red, hairy feathers? bronze, normal feathers?


7. A breeder of hamsters crosses a golden hamster with a black hamster. All the baby hamsters are golden. Which trait is dominant and which is recessive? What are the genotypes of the parents? What are the genotypes of the babies?

8. The breeder takes one of the babies, raises it to maturity, and then mates it to a black hamster. Use a Punnett square to predict the results of this crossbreeding. Predict the genotype(s) and phenotype(s) of the offspring, and the expected ratios.

9. In hamsters, long fur is recessive and short fur is dominant. Suppose the breeder takes a hamster that is heterozygous for both golden fur and short fur, and mates it to a hamster with long black fur. Use a Punnett square to prediict the results of this crossbreeding. Predict the genotype(s) and phenotype(s) of the offspring, and the expected ratios.


10. Humans have four possible blood types (A, B, AB, and O) and these blood types are controlled by three alleles (IA, IB, i). The IA and IB alleles are codominant (they share expression, thus we have an AB blood type), but they are both dominant over the i allele.

A. List the possible genotypes from the phenotypes:
Blood Type A:
Blood Type B:
Blood Type AB:
Blood Type O:

B. A court case has been filed by a mother with type O blood who has a son with type O blood. There are two fathers being accused; one has AB blood and the other A blood. Which one of the men could be the father of the child?

C. In another court case there are three possible fathers. The mother has type B blood, and the child has type O blood. One suspect father has type AB blood, another has type A blood (both his parents were AB), and the third father has type A blood (one parent had AB and one parent had A blood). Construct a pedigree and decide who the father is:


11. Red-green color blindness, in humans, is a sex-linked trait controlled by alleles on the X chromosome. Normal color vision (X+) is dominant to colorblindness (Xc). [NOTE: You could write this as XC for the normal allele and Xc for the recessive colorblind allele. Unfortunately, capital C and lowercase c are hard to tell apart as superscripts, especially in type. Use X+ -- "X-plus" -- for the normal allele.]

A. If a colorblind man marries a woman with normal vision and they have a colorblind son, what are the genotypes of the individuals?

B. If the mother and father were to have more children, what proportion of the girls would be colorblind? Why?


12. Budgies (Melanopsittacus undulatus) are attractive birds that come in many colors. Budgies may produce either or both of two types of pigment in their feathers: a blue pigment and a yellow pigment. Whether or not each pigment is produced is governed by one gene with two alleles. Blue pigment (B) is dominant to no blue pigment (b), and yellow pigment (Y) is dominant to no yellow pigment (y). A budgie that produces neither blue nor yellow pigment in its feathers looks white. A budgie that produces both blue and yellow pigment in its feathers looks green.

A. What is/are the possible genotype(s) of a yellow budgie?
B. What is the phenotype of a budgie with the genotype BbYy?
C. Suppose you cross a homozygous blue budgie with a homozygous white budgie. Predict the results of this cross, both genotype and phenotype.
D. Now suppose you cross one of the offspring from the mating in part C above with a budgie whose genotype is BbYy. Predict the results of your cross. What are the expected genotypes and phenotypes of the offspring from this cross, and in what ratios?