Non-random Mating
In order to satisfy the Hardy-Weinberg equilibrium, individuals within a population must mate at random. However, in actuality, non-random mating appears to be quite common in most population. Breeding territories, courtship displays or hierarchical orders within population are some factors that contribute to contribute to selective mating. When individuals(usually females) are choosy over mates, gene frequencies are also altered. Darwin called this phenomenon sexual selection.
Non-random mating refers to mating that has not occurred due to chance.
Inbreeding
A common result of non-random mating is inbreeding, or mating between closely related partners. An example of this is self-fertilisation or ‘selfing’ in plants, where an egg cell in an ovule of a flower may be fertilized by a sperm cell derived from a pollen grain produced by that same flower.
Inbreeding causes the relative frequencies of genotypes to deviate from that which is expected from Hardy-Weinberg equilibrium. Back to the example on selfing, if dominant (AA) and recessive (aa) individuals self-fertilise, their offspring would be homozygous. However, if heterozygous (Aa) individuals ‘self’, only half their offspring will be heterozygous. The number of heterozygotes decrease while that of dominant and recessive homozygotes increase. Over generation, the frequencies of homozygous genotypes will increase at the expense of heterozygotes.
Inbreeding is generally not recommended because of the existence of deleterious recessive alleles in some populations. Deleterious alleles reduce the likelihood of an individual’s survival and when homozygous, these mutation reduce fitness. Inbreeding will therefore