Genetics Practice - Monohybrids & Dihybrids 

1. A pea plant is the F1 offspring of a true-breeding plant with purple flowers and a true-breeding plant with white flowers. This plant is crossed with one that has white flowers (recessive). How many of the plants in the next generation will have white flowers?

2. In humans, Cystic Fibrosis is caused be a recessive allele on chromosome 7. A person must inherit two of these alleles to have the disease. What are the chances of a child having the disease if both of the parents are heterozygous

3. If attached earlobes are recessive, and the mother has attached earlobes (ee) and the father is a heterozygote (Ee), how many of their children will have attached earlobes?

4. In goats, a recessive gene causes the goats to "faint" when they are startled. A farmer has a goat that is a carrier for the fainting gene (Gg). Gertrude is mated with one that is homozygous dominant. How many of their offspring will be fainters?

5. Test crosses are performed to determine the genotype of an organism. A farmer buys a goat whose owner claims has sired fainting goats, though Gary has never actually fainted himself. What type of goat (genotype/phenotype) should the farmer mate with Gary to determine if Gary really is a carrier. Explain your reasoning showing the cross.

6. In Guinea pigs, short hair is dominant to long hair. Also in Guinea pigs, black eyes are dominant to red eyes. A male guinnea pig that is heterozygous for both traits (HhBb)is crossed with a female that is long haired and red eyed (hhbb). What are the expected phenotypes of their offspring and in what proportion?

7. If both parents are heterozygous for both traits, what are the expected phenotypes of their offspring and in what proportion? You do not need to show the Punnett Square for this one.

8.  In pea plants, purple flowers are dominant to white flowers.    Round seeds are dominant to wrinkled seeds. Do the crosses without a Punnett Square.

Pprr x ppRr

How many offspring are purple with wrinkled seeds? _____

ppRR x Pprr

How many offspring are purple with round seeds? _____

Pprr  x PpRr

How many offspring are white with round seeds? _____

PpRr  x PpRr

How many offspring are white with round seeds? _____