Simple Genetics Practice Problems

2. For each of the genotypes below, determine the phenotype.

Purple flowers are dominant to white.
PP ___________________________
Pp ___________________________
pp ___________________________

Round seeds are dominant to wrinkled.
RR ___________________________
Rr ___________________________
rr ___________________________

Bobtails are recessive (long tails dominant).
TT ___________________________
Tt ___________________________
tt ___________________________

3. For each phenotype, list the genotypes. (Remember to use the letter of the dominant trait)

Straight hair is dominant to curly.
____________ straight
____________ straight
____________ curly
Tail spikes are dominant to plain tails.
____________ pointed
____________ pointed
____________ round

4. Set up the square for each of the crosses listed below. The trait being studied is round seeds (dominant) and wrinkled seeds (recessive)

pea pod

Rr x rr

What percentage of the offspring will be round? _______

Rr x R r

What percentage of the offspring will be round? _______

RR x Rr

What percentage of the offspring will be round? ___________

Practice with Crosses. Show all work!

5. A TT (tall) plant is crossed with a tt (short plant).

What percentage of the offspring will be tall? ___________

6. A Tt plant is crossed with a Tt plant.

What percentage of the offspring will be short? ______

7. A heterozygous round seeded plant (Rr) is crossed with a homozygous round seeded plant (RR).

What percentage of the offspring will be homozygous (RR)? ____________

8. A homozygous round seeded plant is crossed with a homozygous wrinkled seeded plant.

What are the genotypes of the parents? __________ x __________

What percentage of the offspring will also be homozygous? _______ What is the genotype of all of the offspring? ______

9. In pea plants purple flowers are dominant to white flowers.

purple flower

If two white flowered plants are cross, what percentage of their offspring will be white flowered? ______

10. A white flowered plant is crossed with a plant that is heterozygous for the trait.

What percentage of the offspring will have purple flowers? _____________

11. Two plants, both heterozygous for the gene that controls flower color are crossed.

What percentage of their offspring will have purple flowers? ______________
What percentage will have white flowers? ___________


12. In guinea pigs, the allele for short hair is dominant.

guinea pig

What genotype would a heterozygous short haired guinea pig have? _______
What genotype would a purebreeding short haired guinea pig have? _______
What genotype would a long haired guinea pig have? ________

Show the cross for two heterozygous guinea pigs.

What percentage of the offspring will have short hair? ________

What percentage of the offspring will have long hair? _______

Other Resources on Genetics

Peas, Please – practice setting up squares for basic Mendelian traits in pea plants (Key, TpT)

Practice Punnett Squares with Skinny Pigs – hairless guinea pigs are the result of a recessive gene (Key, TpT)

Fruit Fly Genetics (Vg) – practice worksheet on vestigial wing flies (recessive trait)

Explore the Genetics of Corn Snakes – dihybrid crosses with corn snakes, color is polygenic