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 cactuses have spines. Homozygous recessive nn cactuses have no spines at all. A cross between a true-breeding sharp-spined cactus and a spineless cactus would produce ________.
A) all sharp-spined progeny
B) 50% sharp-spined, 50% dull-spined progeny
C) 25% sharp-spined, 50% dull-spined, 25% spineless progeny
D) It is impossible to determine the phenotypes of the progeny.

Question

Quizplus · Accepted Answer

A true-breeding sharp-spined cactus would have the genotype SSNN, and a spineless cactus would have the genotype ssnn. The offspring would all be SsNn, resulting in all sharp-spined progeny.

Gene S Controls the Sharpness of Spines in a Type