two genes, a and b, are linked. an individual of genotype a b / a b is crossed to one that is a b / a b. the f1 is selfed and an f2 is obtained. which of the following ratios most likely represents the phenotypic ratio observed in this f2? a. 1:1:1:1 b. 1:4:4:1 c. 9:3:3:1 d. 51:24:24:1 e. 66:9:9:16