What are the genotypes of the parent cacti

gene A controls the sharpness of spines in a type of cactus. cactuses with the dominant allele, A, have sharp spines, whereas homozygous recessive aa cactuses have dull spines. at the same time, a second gene, N, determines whether cactuses have spines at all. Homozygous recessive nn cactuses have no spines at all.
A) the relationship between genes A and N is an example of?
B) a cactus with sharp spines is crossed with a spineless cactus. all of the offspring have spines but approximately half of the 100offspring have dull spines and half have sharp spines. what are the genotypes of the parent cacti?