(b): A dominant epistatic allele suppresses the expression of a non­allelic gene whether the latter is dominant or recessive. The gene which suppresses the expression of a non­allelic gene is known as epistatic gene. The gene or locus which is suppressed by the presence of non­allelic gene is termed as hypostatic gene. In summer squash or Cucurbita pepo, there are three types of fruit colour – yellow, green and white. White colour is dominant over other colours while yellow is dominant over green. Yellow colour is formed only when the dominant epistatic gene is represented by its recessive allele $(w)$. When the hypostatic gene is also recessive $(y)$, the colour of the fruit is green,

$i.e.$,$W -Yy, W -yy →$ White

$wwY→$  Yellow

$wwyy → $  Green