Gene s controls the sharpness of spines in a type of cactus. cactuses with the dominant allele, s, have sharp spines, whereas homozygous recessive ss cactuses 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

Sharp-spined cactus

Explanation:

Given, that N allele is required for the production of spine and S allele will produce sharp sines.

True breeding sharp spined cactus: NNSS

spineless cactus: nn__ ( we can't fix the allele for second gene since it has not been mentioned as true breeding )

Their progeny: NNSS X nn__ = NnS_

So the progeny is going to be sharp spined because both the dominant alleles N and S are present.

desert perennials often survive by remaining dormant during dry periods of the year, then springing to life when water becomes available. most annual desert plants germinate only after heavy seasonal rain, then complete their reproductive cycle very quickly.