Genetics Problems
1. In sheep white is due to a dominant gene (W), black is due to its recessive allele (W). A
white ewe mated to a white ram produces a black lamb. If they produce another offspring, could
it be white? List the genotypes of all animals mentioned in this problem.
2. In dogs wire hair is due to a dominant gene, smooth hair to its recessive allele. Two wirehaired dogs produce a male pup which is wire haired. To find out most quickly whether he
carries the gene for smooth hair, he should mated to what kind of female?
3. In guinea pigs the coat may be rough (rosetted) or smooth. Certain rough-coated guinea
pigs when crossed with smooth-coated ones produce all rough-coated offspring. Other roughcoated guinea pigs when crossed with smooth-coated ones produce equal numbers of roughcoated and smooth-coated offspring. Smooth-coated guinea pigs crossed together always
produce smooth-coated offspring. Explain these results. Write the genotypes for all animals
concerned in the crosses.
4. In cattle a dominant gene (N) results in a deep notch in each ear. A recessive gene (u)
results, when in the homozygous condition, in an udder abnormality. A farmer has a herd of
cattle in which some of the individuals have notched ears and others have abnormal udders. He
desires to rid his herd of these characters. Which would be more easily eliminated from the
herd? How would he go about the elimination of each?
5. In man normal pigmentation is due to a dominant gene (C), albinism to its recessive allele
(c). A normal man marries an albino woman. Their first child is albino. What are the genotypes
of these three people? If there are more children what will they probably be like?
6. An albino man marries a normally pigmented woman. They have nine children, all
normally pigmented. What are the genotypes of the parents and children?
7. Yellow guinea pigs crossed with white ones always produce cream colored off-spring. Two
cream colored guinea pigs when crossed produce yellow, cream, and white offspring in the ratio
1 yellow; 2 cream; 1 white. How are these colors inherited?
8. In radishes the shape may be long, oval, or round. Crosses between long and oval gave 159
long, 156 oval. Crosses between round and oval gave 199 round, 203 oval. Crosses between
long and round gave 576 oval. Crosses between oval and oval gave 121 long, 243 oval, 119
round. What type of inheritance is involved?
9. In turkeys a dominate gene, R, produces the familiar bronze color; its recessive allele, r,
results in red. Another dominant gene, H, results in normal feathers, it recessive allele, h,
produces feathers without webbing, so that they resemble tufts of hair. Two bronze turkeys with
normal feathers were mated and their offspring consisted of eight bronze with normal feathers,
three bronze with hairy feathers. What were the genotypes of the parents?
10. Assuming the red bird with hairy feathers is a female, what kinds of offspring would you
expect, and in what proportions, if it were mated to its parent?
11. In peas, a gene for tall plants (T) is dominant over its allele for short plants (t). The gene
for smooth peas (S) is dominant over its allele for wrinkled peas (s). Calculate both phenotypic
rations and genotypic rations for the results of each of the following crosses:
TtSs x TtSs
Ttss x ttss
ttSs x Ttss
TTss x ttSS
12. Suppose a child is of a the blood group A and the mother is of group O. What group or
groups may the father belong to?
13. If a man of blood type B, one of whose parents had blood type O, marries a woman with
blood type AB, what will be the theoretical percentage of their children with blood type B?
14. Both Mrs. Smith and Mrs. Jones had babies the same day in the same hospital. Mrs. Smith
took home a baby girl, whom she named Shirley. Mrs. Jones took home a baby girl whom she
named Jane. Mrs. Jones began to suspect, however, that her child had been accidentally switched
with the Smith baby in the nursery. Blood test were made: Mr. Smith was type A, Mrs. Smith
type B, Mr. Jones type A, and Mrs. Jones type A, Shirley was type O, and Jane was type B.
Had a mixup occurred?
15. Red-green color blindness is inherited as a sex-linked recessive. If a color-blind woman
marries a man with normal vision, what would be the expected phenotypes of their children with
reference to this character?