Question

The dominant epistasis ratio is

• A. 9:3:3:1
• B. 12:3:1
• C. 9:3:4
• D. 9:6:1

Answer 1

The correct option is B 12:3:1

• Epistasis occurs when two or more different gene loci contribute to the same phenotype.
• In epistasis, one gene locus masks or modifies the phenotype of a second gene locus. When dominant allele masks the expression of another allele, the dominant allele is an epistatic gene of another gene.
• Dominant gene can express itself only in the presence of another gene. Therefore, it is called dominant epistasis.
• Another gene will only express itself when the recessive trait of the dominant gene is present. Therefore, in 9: 3: 3: 1 ratio both 9 and 3 are expressing the dominant gene and thus the ratio is now 12: 3: 1.

Thus, the correct answer is option B.