Microevolution is the change in allele frequencies that occurs over time within a population.
[1] In population genetics, allele frequencies are used to describe the amount of variation at a particular locus or across multiple loci.
The actual frequency calculations depend on the ploidy of the species for autosomal genes.
If we sample 10 individuals from the population, and we observe the genotype frequencies then there are
Population genetics describes the genetic composition of a population, including allele frequencies, and how allele frequencies are expected to change over time.
The Hardy–Weinberg law describes the expected equilibrium genotype frequencies in a diploid population after random mating.
Random mating alone does not change allele frequencies, and the Hardy–Weinberg equilibrium assumes an infinite population size and a selectively neutral locus.
[1] In natural populations natural selection (adaptation mechanism), gene flow, and mutation combine to change allele frequencies across generations.
Genetic drift causes changes in allele frequency from random sampling due to offspring number variance in a finite population size, with small populations experiencing larger per generation fluctuations in frequency than large populations.
There is also a theory that second adaptation mechanism exists – niche construction[3] According to extended evolutionary synthesis adaptation occur due to natural selection, environmental induction, non-genetic inheritance, learning and cultural transmission.
"ALFRED: an allele frequency database for diverse populations and DNA polymorphisms".