Chapter 7, Problem 39P

In a certain species of flowering plants with a diploid genome, four enzymes are involved in the generation of flower color. The genes encoding these four enzymes are on different chromosomes. The biochemical pathway involved is as follows; the figure shows that either of two different enzymes is sufficient to convert a blue pigment into a purple pigment.

 

A true-breeding green-flowered plant is mated with a true-breeding blue-flowered plant. All of the plants in the resultant F₁ generation have purple flowers. F₁ plants are allowed to self-fertilize, yielding an F₂ generation.

Show genotypes for P, F₁, and F₂ plants, and indicate which genes specify which biochemical steps. Determine the fraction of F plants with the following phenotypes: white flowers, green flowers, blue flowers, and purple flowers. Assume the green-flowered parent is mutant in only a single step of the pathway.