If across between two individuals produces a phenotypic ratio of 9:3:4 in the F2 generation, what type of gene interaction is occurring?

Solution

1. The standard Mendelian dihybrid ratio is $9:3:3:1$.
2. A $9:3:4$ ratio results from the combination of the last two classes ($3+1=4$).
3. This indicates that the recessive genotype at one locus masks the effect of the other locus.
4. This specific interaction is defined as recessive epistasis.
5. Hence the answer is (B).