In contrast to positive and negative selection, selection acts to maintain two or more alleles in a population.

What environmental cues and landmarks do the geese use to determine the timing and direction of their migration over the mountains? how do they find their way?

Amino acids contain the elements carbon, hydrogen, oxygen, nitrogen, and sometimes sulfur. of the 20 amino acids found in humans, 11 are called "nonessential" because they can be manufactured by the body when needed. which elements in these 11 amino acids are commonly obtained from the metabolism of sugar molecules?

Match the functions to the cell types ? contraction and relaxation. conducting electrochemical signals fighting diseases carrying genetic material