Question

In various crosses examining three different Drosophila traits, you find the following ratios: 9:3:4, 9:7, and 12:3:1. What kind of epistasis is each?

Answer 1

The 9:3:4 ratio represents a recessive epistasis, the 9:7 ratio is a duplicate recessive epistasis, and the 12:3:1 ratio is a dominant epistasis.

Step-by-step explanation:

The 9:3:4 ratio represents a recessive epistasis, where the phenotype of one gene masks the phenotype of another gene. In this case, the presence of a recessive allele at one gene (lets call it Gene A) prevents another gene (Gene B) from expressing its phenotype. The ratio of 9:7 represents a duplicate recessive epistasis, where two recessive alleles at either of two genes can mask the phenotype. Finally, the 12:3:1 ratio corresponds to a dominant epistasis, where the presence of a dominant allele at one gene masks the phenotype of another gene.