Simple Genetics Practice Problems

1. For each genotype, indicate whether it is heterozygous (HE) or homozygous (HO)

AA ____ Bb ____ Cc ____ Dd ____

Ee ____ ff ____ GG ____ HH ____

Ii ____ Jj ____ kk ____ Ll ____

Mm ____ nn ____ OO ____ Pp ____

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

Purple flowers are dominant to white flowers PP ___________________________ Pp ___________________________ pp ___________________________	Brown eyes are dominant to blue eyes BB ___________________________ Bb ___________________________ bb ___________________________
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

Pointed heads are dominant to round heads. ____________ 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)

Rr x rr		What percentage of the offspring will be round? ___________
Rr x Rr		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? ______________

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

13. Show the cross for a pure breeding short haired guinea pig
and a long haired guinea pig.
What percentage of the offspring will have short hair? __________

14. 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? _______

15. Two short haired guinea pigs are mated several times. Out of 100
offspring, 25 of them have long hair. What are the probable
genotypes of the parents? ________ x ___________ Show the cross to prove it!