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 coat color in the house mouse. Each gene has two alleles, one of which is dominant for coat color. Genotypes of the form A- B- have a brownish color called agouti, those of the form A- bb are black, and those of the form aa B- and aa bb are albino (white). What ratio of agouti : black : white 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

To solve this problem, we can use a Punnett square. 
```
  | A  a
--|-----
B-|AB AB
b-|Ab Ab
```
When we cross Aa Bb × Aa Bb, we get the following genotypic ratio: 
- 1 AA BB (agouti)
- 2 Aa BB (agouti)
- 1 aa BB (white)
- 2 AA Bb (agouti)
- 4 Aa Bb (agouti)
- 2 aa Bb (black)
- 1 AA bb (black)
- 2 Aa bb (black)
- 1 aa bb (white)

To get the phenotypic ratio, we can group together the individuals with the same coat color: 
- Agouti: 1+2+2 = 5
- Black: 2+4+2 = 8
- White: 1+1 = 2

Therefore, the ratio of agouti : black : white is 5:8:2, which simplifies to 9:3:4. The answer is B.

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