Practice question

A deme is a local interbreeding population: individuals share a geographic area and constitute a reproductive community with appreciable random mating relative to individuals outside the group. In population genetics, the idealized deme is often treated as panmictic, meaning mating is random with respect to genotype within that local unit. This permits allele-frequency models such as Hardy–Weinberg expectations to be applied, while migration connects different demes. Real demes may deviate from perfect random mating because of inbreeding, assortative mating, social structure, or spatial subdivision; the term still emphasizes a local breeding group rather than genetic identity. A group explicitly defined by nonrandom mating contradicts the simplest panmictic ideal. Members also need not possess identical genes, and a fixed dispersal pattern is not part of the definition. Demes are useful units for studying gene flow, drift, local adaptation, and metapopulation structure. Small demes experience stronger genetic drift, whereas migration can homogenize allele frequencies among them. Thus “random mating population” is the closest concise description, with the understood qualification that it is a local population model.