Question

Waxy endosperm (wx), shrunken endosperm (sh), and yellow seedling (v) are encoded by three recessive genes in corn that are linked on chromosome 5. A corn plant homozygous for all three recessive alleles is crossed with a plant homozygous for all the dominant alleles. The resulting F1 are then crossed with a plant homozygous for the recessive alleles in a three-point testcross. The progeny of the testcross are:

Answer 1

The question pertains to genetic linkage in corn and how linked recessive genes influence the phenotypes of offspring in a testcross scenario. It also alludes to epistasis in the context of summer squash fruit color.

Step-by-step explanation:

The question involves the concept of genetic linkage and testcrosses in corn, focusing on how recessive and dominant alleles of linked genes influence phenotypes. In corn, waxy endosperm (wx), shrunken endosperm (sh), and yellow seedling (v) are three recessive genes that are on chromosome 5. When a corn plant with all recessive alleles (wx wx sh sh v v) is crossed with a plant with all dominant alleles, all of the F1 offspring will exhibit the dominant phenotype. If these F1 individuals are testcrossed with a plant homozygous for the recessive alleles, the resulting offspring will show a variety of genotypes and phenotypes that can be used to determine the recombination frequencies and map distances between the linked genes.

In a related example, the color of summer squash is determined by epistasis, where the W gene can mask the expression of the Y gene, resulting in a phenotypic ratio of 12 white:3 yellow:1 green in the offspring of a cross between white heterozygotes for both genes (WwYy x WwYy).