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 fruit shape in summer squash. Each gene has two alleles, one of which is dominant for fruit shape. Genotypes of the form A- B- have disc-shaped fruit, those of the form A- bb and aa B- have sphere-shaped fruit, and genotype aa bb has long fruit. What ratio of disc : sphere : long is expected from the cross Aa Bb × Aa Bb?
A)10:3:3
B)9:3:4
C)12:3:1
D)9:6:1

Question

Quizplus · Accepted Answer

The cross Aa Bb × Aa Bb involves two genes that assort independently, leading to a 9:3:3:1 phenotypic ratio for a dihybrid cross. However, because both A- B- leads to disc-shaped fruit, A- bb and aa B- lead to sphere-shaped fruit, and aa bb leads to long fruit, the phenotypic ratio translates to 9 disc (A- B-), 6 sphere (3 from A- bb + 3 from aa B-), and 1 long (aa bb), resulting in a 9:6:1 ratio.

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