In a diploid cell there are usually two alleles of any one gene (one from each parent).
Within a population there may be many different alleles of a gene; each has a unique nucleotide sequence.
The diameter of the aperture determines the intensity of light admitted. archeology: The study of human history and prehistory through the excavation of sites and the analysis of physical remains, such as graves, tools, pottery, and other artifacts.
The pupil of a human eye is a self-adjusting aperture. archetype: The original form or body plan from which a group of organisms develops.
Also used to describe the process of genetic change within a population, as influenced by natural selection.