Gene S controls the sharpness of spines in a type of cactus. Cacti with the dominant allele, S, have sharp spines, whereas homozygous recessive ss cacti have dull spines. At the same time, a second gene, N, determines whether or not cacti have spines. Homozygous recessive nn cacti have no spines at all. The relationship between genes S and N is an example of which of the following inheritance patterns?
A) incomplete dominance
B) epistasis
C) pleiotropy
D) codominance

Question

Quizplus · Accepted Answer

The relationship between genes S and N is an example of epistasis, where one gene (N) masks the expression of the other gene (S). In this case, the presence of at least one dominant allele of gene N is required for the expression of the S gene, which determines the sharpness of spines. Homozygous recessive nn cacti lack the ability to have spines, regardless of their genotype for gene S.

Gene S Controls the Sharpness of Spines in a Type