In genetics, the dash symbol (-) is a "wild card" that stands for either the dominant allele or the recessive allele; for example, A- means the individual has either the genotype AA or Aa. Two genes that undergo independent assortment affect the shape of the seed capsule in the broadleaf weed known as shepherd's purse. Each gene has two alleles, one of which is dominant for the shape of the seed capsule. Genotypes of the form A- B-, A- bb, and aa B- have triangular seed capsules, whereas the seed capsules of aa bb genotypes are ovoid. What ratio of triangular : ovoid is expected from the cross Aa Bb × Aa Bb?
A)9:7
B)10:6
C)12:4
D)13:3
E)15:1

Question

Quizplus · Accepted Answer

The expected phenotypic ratio for a dihybrid cross Aa Bb × Aa Bb, where both genes show complete dominance and independent assortment, is 9:3:3:1. However, in this case, the genotypes A- B-, A- bb, and aa B- all result in triangular seed capsules, while only aa bb results in ovoid seed capsules. Therefore, the 9:3:3:1 ratio collapses into a 15:1 ratio of triangular to ovoid seed capsules.

In Genetics, the Dash Symbol (-) Is a "Wild Card