Chapter 4, Problem 24P

Blue flower color is produced in a species of morning glories when dominant alleles are present at two gene loci, A and B. (Plants with the genotype A–B– have blue flowers.) Purple flowers result when a dominant allele is present at only one of the two gene loci, A or B. (Plants with the genotypes A–bb and aaB– are purple.) Flowers are red when the plant is homozygous recessive for each gene (i.e., aabb). a. Two pure-breeding purple strains are crossed, and all the ${\text{F}}_{\text{1}}$ plants have blue flowers. What are the genotypes of the parental plants? b. If two ${\text{F}}_{\text{1}}$ plants are crossed, what are the expected phenotypes and frequencies in the ${\text{F}}_{\text{2}}$? c. If an ${\text{F}}_{\text{1}}$ plant is backcrossed to one of the pure-breeding parental plants, what is the expected ratio of phenotypes among progeny? Why is the phenotype ratio the same regardless of which parental strain is selected for the backcross?