Question

A dihybrid phenotypic ratio of 15:1 was obtained while making a cross of AaBb × AaBb. This is an example of:

• A. Cytoplasmic inheritance
• B. Incomplete dominance
• C. Complete dominance and epistasis
• D. Co-dominance

Hint:

The 15:1 ratio is a classic example of epistasis, where one gene masks the effect of another gene at a different locus.

Answer 1

The Correct Option is C

Step 1: Understanding the phenotypic ratio.
In a dihybrid cross of the form AaBb × AaBb, the expected phenotypic ratio for complete dominance should be 9:3:3:1. However, a 15:1 ratio indicates the involvement of an epistatic gene. In this case, one gene (which can be epistatic) masks the expression of another.

Step 2: Analyzing the options.
- (A) Cytoplasmic inheritance: Cytoplasmic inheritance does not produce a 15:1 ratio.
- (B) Incomplete dominance: Incomplete dominance results in a phenotypic ratio of 1:2:1.
- (C) Complete dominance and epistasis: Correct — The 15:1 ratio is characteristic of epistasis, where one gene masks the expression of another.
- (D) Co-dominance: Co-dominance results in both alleles being expressed, which would not lead to a 15:1 ratio.

Step 3: Conclusion.
The correct answer is (C): Complete dominance and epistasis.