Arecessive allele a. occurs as a regulatory gene only b. needs to be present on only one chromosome to be expressed c. is never expressed d. needs to be present on both chromosomes to be expressed

D: needs to be present on both chromosomes to be expressed

Why: Because if there was a dominant trait present, then the dominant trait would overpower the recessive trait regardless of the matter.

it enhances antibody production by t cells of the adaptive immune system.

hope i'm right

explanation:

a

explanation:

many plants naturally reproduce this way, but it can also be induced artificially. horticulturalists have developed asexual propagation techniques that use vegetative plant parts to replicate plants. success rates and difficulty of propagation vary greatly. monocotyledons typically lack a vascular cambium and therefore are harder to propagate.