Allele frequency

Allele frequency is the proportion of copies of a particular allele among all allele copies at a genetic locus in a population. It describes genetic variation without distinguishing individuals who carry one copy from those who carry two.

Hardy–Weinberg principle: A model relating allele and genotype frequencies in a large, randomly mating population without evolutionary forces. It predicts genotype proportions from allele frequencies under its idealized conditions.
Allele: One of two or more alternative DNA sequences found at a particular genetic locus. Allele frequency tracks copies of a specific alternative at a locus.
Allele frequency spectrum: A distribution describing how many genetic variants occur at different frequencies in a population. It summarizes many allele frequencies to reveal demographic and evolutionary patterns.
Founder effect: A shift in genetic variation when a population is established by a small number of individuals. Founding individuals can make some alleles unusually frequent in descendants.
Allele frequency differentiation: A measure of how allele frequencies vary among populations. It compares populations rather than describing one population's allele proportions.
Genetic drift: Random changes in allele frequencies caused by chance differences in reproductive success. Sampling chance can shift frequencies, especially in small populations.
Gene locus: A specific position or region on a chromosome where a genetic sequence is located. A frequency is defined for alleles at a particular locus.
Single-nucleotide polymorphism: A common genetic variant in which individuals differ at one DNA nucleotide position. Its alternative alleles can be counted to estimate variation across populations.
Bottleneck effect: A reduction in genetic variation after a population shrinks sharply in size. A bottleneck can change allele frequencies through chance sampling.
Linkage disequilibrium: A nonrandom association of alleles at different genetic loci in a population. It concerns associations between loci, not the frequency of one allele alone.

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