Genetic equilibrium occurs when A. the number of new alleles equals the number of extinct alleles.
B. there is a high frequency of non-random mating.
C. populations are very small.
D. there is no change in the allele frequencies within a species.

Lactase is essential for digesting lactose in milk. this enzyme is specific for this sugar. why? molecules and active sites vary in size; only properly sized molecules can fit. there is a precise compatibility between the active site and the lactose molecule. specificity refers to the action of the enzyme, such as hydrolysis, and relatively few molecules can be hydrolyzed. reaction-specific enzymes assume a fit by folding around the most numerous substrate molecules.