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 n n 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.

In gene S which control the sharpness of spines in type of cactuses with the dominant allele S which have sharp spines and homologous recessive aa cactuses have dull spines.

N, determine are not cactuses have spines. Homozygous recessive nn cactuses have no spines. N allele is required for the production of spine and S allele will produce sharp sines.

Epistatsis is form of gene interaction by which gene on one locus modifies or suppresses the effect of another gene on separate locus.Recessive epistasis occur when a recessive allele at one locus suppresses the expression of alleles on separate locus/ loci.

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