A 13:3 ratio is obtained from the cross Aa Bb ×Aa Bb.What phenotypic ratio is expected if an Aa Bb individual is testcrossed (Aa Bb × aa bb)?

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When an individual with the genotype Aa Bb (a heterozygote for two different traits) is testcrossed with an individual with the genotype aa bb (a homozygote recessive for both traits), the possible gametes from the Aa Bb individual are AB, Ab, aB, and ab. The possible gametes from the aa bb individual are ab only. The offspring will have a 1:1:1:1 ratio for the four possible combinations AB, Ab, aB, and ab, as each gamete from the Aa Bb parent has an equal chance of combining with the ab gamete from the aa bb parent. This results in a 3:1 phenotypic ratio for each trait (i.e. 3 dominant: 1 recessive).

A 13:3 Ratio Is Obtained from the Cross Aa Bb