Genetics Practice Problems 1. For each genotype below, indicate whether it is heterozygous (He) or homozygous (Ho) AA _____ aa ______ Pp ______ pp ______ Aa ______ BB ______ 2. For each of the genotypes below determine what phenotypes would be possible. Red eyes are dominant to white, Tall plants are dominant to short. RR ______ Rr ______ rr ______ TT ______ Tt ______ tt ______ 3. For each phenotype below, list all of the possible genotypes (remember to use the letter of the dominant trait) Brown fur is dominant to white, purple flowers are dominant to white. Brown fur _________________ White fur ________________ Purple flowers ___________________ White flowers ___________________ Use a Punnett Square to solve the following problems: 4. A guinea pig with short hair (SS) is bred to a guinea pig with long hair (ss). How many of the offspring will have short hair? Show your work. 5. In pea plants purple flowers are dominant to white. Two heterozygous, purple flowered pea plants are crossed. What is the genotypic ratio? Show your work. 6. Round peas are dominant to wrinkled in pea plants. You have a plant that produces round peas, but you do not know the genotype. You perform a testcross and get 50% round and 50% wrinkled peas. What is the genotype of the round-seeded parent? Show the testcross. 7. Two purple flowered pea plants are crossed together. Out of 100 offspring, 25 are white. What are the genotypes of the parents? Show your work. The following problems deal with two traits – use the 16-square Punnett Square! In rabbits, grey hair is dominant to white hair. Also in rabbits, black eyes are dominant to red eyes. KEY: GG = gray hair Gg = gray hair gg = white hair BB = black eyes Bb = black eyes bb = red eyes 8. What are the phenotypes (descriptions) of rabbits that have the following genotypes: Ggbb ____________________ ggBB ________________________ ggbb ____________________ GgBb _________________________ 9. A male rabbit with the genotype GGbb is crossed with a female rabbit with the genotype ggBb The square is set up below. Fill it out and determine the phenotypes and proportions in the offspring. How many out of 16 have grey fur and black eyes? ______ How many out of 16 have grey fur and red eyes? ________ How many out of 16 have white fur and black eyes? ______ How many out of 16 have white fur and red eyes? _______ 10. A male rabbit with the genotype GGBb . Determine the types of gametes produced by this rabbit (the sperm would have these combinations of alleles) Hint there are 4 combinations. 11. A female rabbit has the genotype GgBb. Determine the types of gametes (eggs) produced by this rabbit. 12. Use the gametes from #10 and #11 to set up the Punnett square below. Put the male's gametes on the top and the female's gametes down the side. Then fill out the square and determine what kind of offspring would be produced from this cross and in what proportion. 13. An aquatic arthropod called a Cyclops has antennae that are either smooth or barbed. The allele for barbs is dominant. In the same organism, resistance to pesticides is a recessive trait. Make a "key" to show all the possible genotypes (and phenotypes) of this organism. Use the rabbit key to help you if you're lost. Key: 14. A Cyclops that is resistant to pesticides and has smooth antennae is crossed with one that is heterozygous for both traits. Show the genotypes of the parents. ______________ x _______________ 15. Set up a Punnett square for the cross. 16. What are the phenotypic ratios of the offspring? Use the following list of traits for ball pythons for the next set of questions: Albino is a recessive mutation (a) Piebald is a recessive mutation (p) Pinstripe is a dominant mutation (S) 17. An albino heterozygous for piebald is crossed with a piebald heterozygous for albino. What are the genotypes of the parents? 18. Show the cross: 19. A pinstripe het for albino is bred to a normal patterned albino. The offspring are all pinstriped. What are the genotypes of the parents? 20. Show the Punnett Square and ratio of phenotypes that result from this cross. Extra Credit: If you cross a heterozygous pinstripe heterozygous for both albino and piebald and a normal pattern albino het for piebald, what is the probability of getting a hatchling that shows all three traits?