Punnett Squares and Dihybrid Crosses

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Punnett Squares and Dihybrid Crosses 2017-11-09T09:08:57+00:00

The Punnett square also allows the determination of genotypes and phenotypes from dihybrid crosses. However, this process works only if the genes are independent of each other, that is, they are not linked, and they segregate independently of each other during meiosis.

According to Mendel’s Second Law, the Law of Independent Assortment, the inheritance of one trait will not affect the inheritance of another, meaning that alleles of each gene separate independently during gamete formation.

Heterozygous Dihybrid Cross
The phenotypes of the offspring from a heterozygous dihybrid cross with two independent traits, such as the RrYy x RrYy example, show a 9:3:3:1 ratio. In a cross involving pea plants heterozygous for green flat pods (GgFf), 9/16 plants have green flat pods, 3/16 have green constricted pods, 3/16 have yellow flat pods, and 1/16 have yellow constricted pods.

Summary
A dihybrid cross-examines the inheritance of two traits at the same time.
Dihybrid crosses are more complicated than monohybrid crosses.
With unlinked genes, a 9:3:3:1 phenotypic ratio will result in the offspring of a cross of two completely heterozygous individuals.

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