Biology 22 Mendelian Genetics Problems

  1. Consider the following two unlinked genes in the poisonous plant, Jimson Weed. The dominant allele V produces violet petals while the recessive allele v produces white petals. The dominant allele P produces prickly capsules while the recessive allele p produces smooth capsules. A true-breeding violet, smooth plant is crossed to a true-breeding white, prickly plnat. What is the genotype and phenotype of the F1 individuals? The F1 individuals are crossed to each other to produce an F2 generation. What hare the phenotypes and frequencies of the offspring in the F2 generation?
  1. Retinitis pigmentosum, a progressive degeneration of the retina, is an X-linked recessive trait in humans. Adam does not have retinitis pigmentosum. He marries Barbara, who also does not have the disease. Barbara’s father, however, does have retinitis pigmentosum. What are the genotypes, phenotypes and frequencies of the expected offspring for Adam and Barbara?
  1. Phenylketonuria, PKU, is a neurodegenerative disorder resulting from the inability to metabolize phenylalanine. PKU is inherited as an autosomal recessive trait. Jack does not have PKU but he has a sister who is afflicted with the condition. Jill also does not have PKU but she has a brother with the disease.

a. What is the probability that Jack and Jill will have a daughter with PKU?

b. What is the probability that Jack and Jill’s first child will have PKU, their second child will not have PKU and their third child will have PKU?

c. Out of four children born to Jack and Jill, what is the probability that two children will have PKU?

d. Suppose Jack and Jill’s first child is born with PKU. Using this information, what is the probability that their next child will be a son with PKU?

e. Suppose Jack and Jill’s first child is born with PKU. Using this information, what is the probability that out of three children, two will have PKU?

  1. In rabbits, coat color is affected by a series of alleles with a hierarchy of dominance such that C+>Cch>Ch>C. Each allele is dominant over all the alleles listed to its right. C+ codes for full color, Cch codes for chinchilla, Ch codes for himalayan (white with black extremities) and C codes for albino. A chinchilla rabbit is mated to a himalayan rabbit. Each of these rabbits had one albino parent. What are the phenotypes of the offspring and in what frequencies will they be produced?
  1. The autosomal dominant allele ML specifies a tailless phenotype in cats. This allele is lethal in the homozygous state. A tailless female cat is mated to a tailless male cat. What are the phenotypes of the offspring and in what frequencies will they be produced?

6. In chickens, two genes affect the shape of the comb. Chickens with at least one copyof both dominant alleles, R_P_, have a walnut comb. Chickens with at least one copy of the P allele, rrP_, have a pea comb. Chickens with at least one copy of the R allele, R_pp, have a rose comb. Chickens with no dominant alleles, rrpp, have a single comb. A walnut-combed rooster is mated to a rose-combed hen. Each of these chickens had one parent with a single comb. What are the phenotypes of the offspring and in what frequencies will they be produced?