Genetics

1. A diploid cell contains three pairs of homologous chromosomes designated C1 and C2, M1 and M2, and S1 and S2. No crossing over occurs.

a. What combination(s) of chromosomes are possible in daughter cells following mitosis?

b. What combination(s) of chromosomes are possible in haploid cells following both divisions of meiosis? (Hint: remember independent assortment)

2. A recessive mutant allele, black, causes a very dark body in Drosophila when homozygous. The normal wild-type color is gray.

a. A black female is crossed to a heterozygous gray male. What are the parental genotypes?

b. What F1 phenotypic and genotypic ratios are produced from this cross? (Show your Punnett Square)

3. R codes for red flower color and r codes for white flower color.

a. What color would Rr be if R has complete dominance?

b. What color would Rr be if R and r are codominant?

c. What color would Rr be if R has incomplete dominance?

4. Red-green colorblindness is an X-linked recessive mutation. A colorblind female is crossed with a normal male.

a. What are the parental genotypes? (Hint: the sex of the parent is important)Diagram the F1 results from this cross. (Show the Punnett Square).

b. Diagram the F2 results. (Show the Punnett Square). (5 points) In a dihybrid cross between RrTt and RRtt, what are the genotype and phenotype ratios of the offspring, assuming R and T are dominant? R codes for round seed, while r codes for wrinkled seed. T codes for tall height, while t codes for short height. (Show the Punnett Square).

5. The pedigree below traces the inheritance of alkaptonuria, a biochemical disorder. Affected individuals, indicated here by the filled-in circles and squares, are unable to break down a substance called alkapton, which colors the urine and stains body tissues.

a. Does alkaptonuria appear to be caused by a dominant or recessive allele? Explain.

b. What is George’s phenotype?

c. Is it possible for Daniel to have a child with alkaptonuria? Explain.

d. How would knowing the pattern of inheritance influence the treatment plan for this disease?

6. Mary has type A blood and her husband has type B blood. Her husband’s parents both had type AB. They have three children, one with type A, one with type AB, and one with type B. Relatives suspect that one of the children was adopted.

a. What are the parent’s blood genotypes?

b. Which child was adopted? Explain your answer.