Mendelian Genetics Problem Set
Please write all answers and SHOW ALL WORK on a separate sheet of paper.
1. In rabbits the allele for black coat color (B) is dominant over the allele for brown coat color (b). What would be the results of a cross between an animal homozygous for black coat color (BB) and one homozygous for brown coat color (bb)? Show the gametes, Punnett square, and phenotypic and genotypic ratios.
2. Cystic fibrosis is a recessively inherited genetic disorder, in which a recessive gene codes for a faulty non-working membrane protein whose job is to pump chloride ions out of lung cells. Individuals who lack these functional membrane proteins accumulate mucus in their lungs and usually don’t survive to adulthood. You are a genetic counselor. A worried couple (Tom and Nicole), with a family history of cystic fibrosis, comes to your office for advice as to whether they should have children or adopt. After charting their family history, you conclude that Tom is heterozygous (a “carrier”) for cystic fibrosis and Nicole is homozygous dominant. What advice would you give them? (Show the Punnett square you used to come to your decision.)
3. The urine of people has a distinctive odor after eating asparagus . This appears to be a trait due to a gene coding for an enzyme that breaks down one of the chemicals in asparagus. However, only some people have the ability to smell it. The ability to detect the smell dominates over not having the ability to detect it. If a homozygous recessive person marries a person heterozygous for this trait, what phenotypic and genotypic ratio will their children theoretically exhibit? Use A and a for alleles.
4. In cabbage butterflies, white color (A) is dominant and yellow color (a) is recessive. If a pure white cabbage butterfly mates with a yellow cabbage butterfly, all the resulting butterflies are heterozygous white. What are the genotypes of the parents and children?
5. Freckles are dominant to no freckles. A man with freckles and a woman with no freckles have 3 children with freckles and one with no freckles. What are the genotypes of the parents and children?
6. Lactose is a sugar that is found in dairy products. Lactose intolerance is inherited as an autosomal (a gene on a non-sex chromosome) dominant trait. People who have an allele for lactose intolerance cannot properly digest milk products. Paul is intolerant of lactose but his wife, Laura, is not. Additionally, Paul's dad is lactose intolerant but his mom is not. From this information about his family, you realize that Paul is heterozygous (Aa) for the lactose intolerance trait.
(a) Based on the information about Paul’s parents, explain how you realized Paul must be heterozygous.
(b) Knowing Paul's genotype, what alleles can he pass on to his offspring?
(c) What is the probability that Paul and Laura will have a girl that is intolerant of lactose?
7. You have some pea plants with yellow seeds, but don't know whether they are pure or hybrids. In peas yellow seeds are dominant over green seeds. Show on Punnett diagrams how you would do a testcrossto determine whether plants with yellow seeds are pure or hybrid.
8. In Guinea pigs rough and black are dominant. A rough-coated, black guinea pig, whose mother was smooth and white, is mated with a smooth, white guinea pig. What kinds of offspring would they produce and in what relative numbers?
9. Mating a red-eyed fly with curved wings and a brown-eyed fly with straight wings yields f1 all red-eyed and straight wings. What kinds of flies would you expect in f2? In what relative numbers?
10. What is the probability that the following pairs of parents will produce the indicated offspring? AABbCc x AaBbCc AAbbCC