Practice Mendelian Genetics
1. In tomatoes, red fruit is dominant to yellow fruit. A true breeding red-fruited plant is bred to a truebreeding yellow-fruited plant.
a. What are the phenotypes would you expect to see in the F1 offspring?
b. If two of the F1 plants were bred, what phenotypes would you expect to see in the F2
offspring?
c. What genotypes would you expect to see in the F2 offspring?
2. A brown mouse is mated to a white mouse and all of their offspring are brown.
a. Give symbols for the possible alleles. Which allele is dominant?
b. What are the genotypes of the mice that were mated?
c. If two of the F1 brown offspring are mated together, what percentage of the F2 mice will be
brown?
3. A genetic cross between two F1-hybrid pea plants having yellow seeds will yield what percent greenseeded plants in the F2 generation? Yellow seeds are dominant to green.
4. In pea plants, tall is dominant over short. An F1 plant that is homozygous recessive is crossed with a
heterozygous F1 plant. Use a punnett square to answer the following questions.
a. What percentage of the seeds from the cross will be homozygous dominant?
b. What percentage of the seeds from the cross will be heterozygous?
c. What percentage of the seeds from the cross will be homozygous recessive?
d. What percentage of the seeds from the cross will produce a tall plant?
e. What percentage of the seeds from the cross will produce a short plant?
5. A pure-breeding tall pea plant is crossed with a pure-breeding short pea plant. All of the offspring of
this cross are tall.
a. Suppose two of the offspring of the F1 are crossed and produce 1000 offspring. How many tall
and how many short will you expect?
Answers
1. a. 100% red
b. 75% red, 25% yellow
c. 25% RR, 50% Rr, 25% rr
2. a. B = brown (dominant), B = white
b. Bb x Bb
c. 75% brown
3. Among the F2 plants of a Yy x Yy cross, 25% will be yy with the recessive, green-seeded phenotype
4. a. 0%
b. 50%
c. 50%
d. 50%
e. 50%
5. a. We would expect ¾ of the offspring to be either TT or Tt, so 750 tall; ¼ should be short, or 250.