20. Quantitative Genetics

Consider a true-breeding plant, AABBCC, crossed with another true-breeding plant, aabbcc, whose resulting offspring are AaBbCc. If you cross the F₁ generation, and independent assortment is operational, the expected fraction of offspring in each phenotypic class is given by the expression N!/M!(N−M)! where N is the total number of alleles (six in this example) and M is the number of uppercase alleles. In a cross of AaBbCc×AaBbCc, what proportion of the offspring would be expected to contain two uppercase alleles?

Floral traits in plants often play key roles in diversification, in that slight modifications of those traits, if genetically determined, may quickly lead to reproductive restrictions and evolution. Insight into genetic involvement in flower formation is often acquired through selection experiments that expose realized heritability. Lendvai and Levin (2003) conducted a series of artificial selection experiments on flower size (diameter) in Phlox drummondii. Data from their selection experiments are presented in the following table in modified form and content.

Considering that differences in control values represent year-to-year differences in greenhouse conditions, calculate (in mm) the average response to selection over the three-year period. <>