Biology as Poetry: Genetics

Bacteriophage Ecology Group

Dihybrid Cross

Matings between individuals which are equivalently heterozygous at two different loci.

One can depict a dihybrid cross, for example, as AaBa × AaBa. The progeny of such a cross will include AABB, AaBa, AABa, AaBB, Aabb, AAbb, aaBa, aaBB, and aabb. See by contrast the much simpler situation of a monohybrid cross.

Given independent assortment of the two loci in question, dominant-recessive relationships between the alleles found at each locus, and no epistasis, then the phenotypic ratio associated with the resulting genotypes will be 9:3:3:1! That is, in the above example and assuming that uppercase alleles are dominant to lowercase alleles, then 9 AB, 3 Ab, 3 aB, and 1 ab.

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