Question

In some primroses, the petal color blue is dominant. A cross between a true-breed blue primrose and a white primrose yields progeny with white petals. A second gene at another locus prevented the expression of the dominant coat color. This is an example of ______.

a) Polygenic inheritance
b) Pleiotropy
c) Epistasis
d) Incomplete dominance

Answer 1

The phenomenon where a second gene at another locus prevents the expression of a dominant gene, as seen in the white progeny of true-breed blue primroses, is called epistasis.

Step-by-step explanation:

In some primroses, a cross between true-breed blue primrose (dominant for petal color) and white primrose led to progeny with white petals due to a second gene preventing the expression of the dominant blue color. This is an example of epistasis, where one gene interferes with the expression of another gene. A similar example of epistasis can be seen in mice, where the coat color is dependent on two genes. The agouti color is dominant, but a second gene is required for pigment production. Mice with the recessive allele of this second gene are albino, showing that the phenotype is not simply determined by the first gene's alleles. In conclusion, epistasis occurs when the phenotypic effect of one gene's alleles is modified by another gene.