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, tongue rolling is a dominant trait, those with the recessive condition cannot roll their tongues. Grant can roll his tongue, but his mother could not. What is Grant's genotype? ______

Grant marries Sam, but Sam cannot roll her tongue. What proportion of their children will be tongue rollers?



3. Two parents who can roll their tongues have a child who cannot. What are the parents' genotyps?


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?

guinea pig


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.

flowerPprr 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 wrinkled seeds? _____