Question

1. Assume that tail length in mice is a quantitative trait involving two genes, each with 2 alleles. One allele at each gene contributes to long tails, the other allele at each gene does not (small tails). The genes are located on different autosomes. Mice with 0 contributing alleles have tails that are 4 cm in length; mice with tails with 4 contributing alleles are 12 cm in length. Determine the phenotypic ratio from an F2 from a true breeding parent with 0 contributing alleles and a second true breeding parent with 4 contributing alleles.

ANSWER:

1. A woman with type A blood marries a man with type B. They have three children; one has type O and the other 2 have type A. Determine the genotypes of the parents and the children.

ANSWER:

1. In some varieties of squash, two genes (A and B) are involved in the expression of shape; each gene is completely dominant. Interaction between the two loci produces a new phenotype. Long fruit are homozygous recessive for both genes. Sphere shaped fruit are homozygous recessive for one of the genes, and have at least one dominant allele for the other gene. Finally, disk shaped fruit have at least one dominant allele for both genes. (8 pts)

1. A cross between two sphere shaped fruit produces offspring in the proportions ¼ disk shaped, ½ sphere shaped, ¼ long. Determine the parents of this cross.

ANSWER:

1. Cross a long fruited plant with a sphere shaped fruit that is heterozygous for the A gene and homozygous recessive for the B gene. List the proportions of the phenotypes you would expect.

ANSWER:

1. A hypothetical alien trait is controlled by four different alleles of a single gene: a, a’, a’’ and A. An alien is a diploid organism.

The phenotype associated with the alleles is as follows:

A = 4 fingers

a” = 3 fingers

a’ = 2 fingers

a = 1 finger

The order of dominance of the alleles is A > a”> a’ > a. How many different genotypes are possible? List them. Give the phenotype for each genotype.

ANSWER:

1. The allele for Tay Sachs disease is a recessive lethal allele in humans. Using a Punnett square, show how two normal parents could have a child with Tay Sachs. What is the probability of these two parents having a child with Tay Sachs?

ANSWER:

Answer 1

QUESTION 1

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