Question

The ratio 9:3:3:1 represents:

• A. Mendel’s dihybrid phenotypic ratio
• B. Mendel’s monohybrid phenotypic ratio
• C. Mendel’s monohybrid genotypic ratio
• D. Mendel’s dihybrid genotypic ratio

Answer 1

In a cross involving different seed shape alleles (round, R, and wrinkled, r) and different seed color alleles (yellow, Y, and green, y), four types of gametes are expected: RY, Ry, rY, and ry. Therefore, in the F2 generation there are 16 possible combinations of alleles, each of them equally probable. The hypothesis that color and shape genes assort independently thus predicts that the F2 generation will display a 9:3:3:1 phenotypic ratio: nine individuals with round, yellow seeds, three with round, green seeds, three with wrinkled, yellow seeds, and one with wrinkled, green seeds.