What would be the genotype of the parents if the offspring have the phenotypes in 1:1 proportion?

Options

A. `Aa xx Aa`
B. `A A xx A A`
C. `Aa xx A A`
D. `Aa xx a a`

Answer

D

Explanation

50% of all offspring should have the aa genotype. A testcross to a heterozygous individual should always yield about a 1:1 ratio of the dominant to recessive phenotype. So, both the genotypic and phenotypic ratios here are 50:50.