Inheritance of fruit color in summer squash
provides an example of the phenomenon of
epistasis. Yellow fruit is produced by a cross
involving the homozygous recessive
expression of the W gene (ww]) and either
the homozygous dominant (YY) or
heterozygous (Yy) form of the Y) gene. The
wwyy outcome is green fruit. White fruit
arises whenever a dominant copy of the W
gene is involved in the cross, regardless of
the Y alleles present.
A cross of white WwYy heterozygotes
produces the phenotypic ratio of 12 white : 3
yellow: 1 green fruits. Determine the best
explanation for how these outcomes occur.