Chapter 4, Problem 19P

Feather color in parakeets is produced by the blending of pigments produced from two biosynthetic pathways shown below. Four independently assorting genes (A, B, C, and D) produce enzymes that catalyze separate steps of the pathways. For the questions below, use an uppercase letter to indicate a dominant allele producing full enzymatic activity and a lowercase letter to indicate a recessive allele producing no functional enzyme. Feather colors produced by mixing pigments are green (yellow + blue) and purple (red + blue). Red, yellow, and blue feathers result from production of one colored pigment, and white results from absence of pigment production.

a. What is the genotype of a pure-breeding purple parakeet strain?

b. What is the genotype of a pure-breeding yellow strain of parakeet?

c. If a pure-breeding blue strain of parakeet (aa BB CC DD) is crossed to one that is pure-breeding purple, predict the genotype(s) and phenotype(s) of the ${\text{F}}_{\text{1}}$. Show your work.

d. If ${\text{F}}_{\text{1}}$ birds identified in part (c) are mated at random, what phenotypes do you expect in the ${\text{F}}_{\text{2}}$ generation? What are the ratios among phenotypes? Show your work.