If A is dominant to a and B is dominant to b, what is the expected phenotypic ratio of the cross AaBb × AaBb?
A) 16:0:0:0
B) 8:4:2:2
C) 1:1:1:1
D) 9:3:3:1

Question

Quizplus · Accepted Answer

The expected phenotypic ratio can be determined by using the FOIL method, which means multiplying the First terms, Outer terms, Inner terms, and Last terms of the two genotypes, AaBb × AaBb.

First terms: AA (homozygous dominant) - 1 possible genotype
Outer terms: AB and aB (heterozygous dominant for A and B) - 2 possible genotypes
Inner terms: Ab and Ab (heterozygous dominant for A and b) - 2 possible genotypes
Last terms: aa (homozygous recessive) - 1 possible genotype

Therefore, the expected phenotypic ratio is 9:3:3:1 (9 dominant for both traits, 3 dominant for only one trait, 3 dominant for the other trait, and 1 recessive for both traits), which is the ratio for a dihybrid cross.

If a Is Dominant to a and B Is Dominant