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Introduction to Mendelian Genetics

Author(s): Lisa M. Meffert, PhD

Crossing the F1 Generation: Female Contribution

Next, write in the female's allelic contributions to the potential offspring. In this case, there are three possible genotypes, in the ratio 1:2:1, for the TT, Tt, and tt combinations, respectively (note that Tt is the same as tT). Since the T allele is dominant to the t allele, every individual with at least one T has the tall phenotype. Only individuals homozygous for "t" will be short. Thus, we find that the phenotypes of the offspring are in the ratio of 3:1 for tall and short, respectively.

Note how this particulate model of inheritance maintains variation. Under the blending model of inheritance, one would expect a mating of two tall individuals to produce only tall offspring. Instead, the crossing of the F1 recovered the variation in the parental lines.