Last week’s post on The Hardy-Weinberg Equlibrium and its Implications covered the five external forces that shift that equilibrium to cause a change in gene and genotypic frequencies: selection; gene mutations; migration in and out of a population; random genetic drift; and non-random matings.
Three of these are controllable by breeders and routinely applied in breeding programmes: selection; migration in and out; and non-random matings.
The other two — gene mutations and random genetic drift — are completely random forces beyond anyone’s control, and patterns of inheritance are ultimately down to the sheer chance of gene segregation during meiosis and ‘luck of the draw’.
Gene mutations are extremely rare events and, should they even occur at all, are as likely to have good, bad or indifferent effects . Any mutation that does appear is most likely to be of a single allele, as the chance of two or more mutations occurring simultaneously, much less being inherited together, is even more remote. Such an allele, or any other rare allele for that matter, may then be subject to that other random force: random genetic drift.
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