Question

What is the characteristic genetic ratio of a dihybrid cross involving dominant epistasis?

• A. 9:3:3:1
• B. 12:3:1
• C. 9:7
• D. 15:1

Hint:

Dominant epistasis modifies the classic 9:3:3:1 ratio to 12:3:1 by masking one gene's effect with a dominant allele of another gene.

Answer 1

The Correct Option is B

Concept: Epistasis is the interaction between genes where one gene masks or modifies the expression of another. In dominant epistasis, a dominant allele of one gene masks the effect of another gene.
Step 1: Understanding dominant epistasis.}
In dominant epistasis, the presence of at least one dominant allele (A-) suppresses the expression of another gene (B/b), regardless of its alleles.
Step 2: Determining phenotypic ratio.}
A typical dihybrid cross (AaBb $\times$ AaBb) under dominant epistasis produces a modified phenotypic ratio: \[ 12 : 3 : 1 \]
Step 3: Explanation of ratio.}

• 12 – Individuals with dominant epistatic allele (A-)
• 3 – Individuals with aaB-
• 1 – Individuals with aabb