In a Perfectly Controlled Laboratory Environment,a Pure-Breeding Fish with a 23-Mm

Essay

In a perfectly controlled laboratory environment,a pure-breeding fish with a 23-mm tail was crossed to a pure-breeding fish with a 15-mm tail.In the F₁,all individuals had tails of an intermediate length: 19 mm.If tail length is a typical polygenic trait controlled entirely by the equal and additive effect of two unlinked genes,each with two alleles ("+" and "-"),what phenotypic ratios do you expect to find in the F₂?