You cross two strains of pea plants, both true-breeding. One has purple flowers (dominant) and the other has white flowers (recessive). What is the expected ratio of phenotypes in the next generation?

Question

You cross two strains of pea plants, both true-breeding. One has purple flowers (dominant) and the other has white flowers (recessive). What is the expected ratio of phenotypes in the next generation?

A. All purple

B. all pink (light purple)

C. Three purple : one white

D. One purple : two pink (light purple) : one white

Answer 1

The definition of a true-breeding organism is that it passes its phenotypical traits to its offspring for many generations, therefore it must be homozygous. Thus, the plant with purple flowers has a homozygous dominant genotype, and its allele combination will be AA. The plant with white flowers has homozygous recessive genotype, and its allele combination will be aa. All resulting zygotes will have the same heterozygous genotype Aa, which means that phenotypically, all plants will be purple (dominant genotype).