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 flower color in sweet peas. Each gene as two alleles, one of which is dominant for flower color. Genotypes of the form A- B- have purple flowers, whereas those of the form A- bb, aa B-, and aa bb have white flowers. What ratio of purple : white 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

When we cross Aa Bb × Aa Bb, we can use a Punnett square to determine the possible genotypes and corresponding phenotypes of the offspring.

|   | A  | a  |
|---|---|---|
| B | AB  | aB |
| b | Ab | ab |

We can see that there are 9 possible genotypes that result in purple flowers and 7 possible genotypes that result in white flowers. Thus, the expected ratio of purple : white is 9:7.

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