Genetic drift [HD Animation]


random genetic drift allows allele frequencies to change over time due to chance the smaller a population is the more susceptible it is to dramatic changes in allele frequencies due to genetic drift in small populations genetic drift favors a relatively rapid loss of alleles leading to one allele becoming the only allele remaining for a particular gene this is called fixation of the allele consider a hypothetical situation where a gene has two alleles capital A and lowercase a each allele is present at the start and a frequency of 0.5 we will follow the frequency for the capital a allele if the starting population is 20 and is sampled from by random mating to produce a new generation of 20 individuals then dramatic changes in allele frequency are likely for this sampling as the process continues for future generations the capital a allele is quickly lost meaning that the lowercase a allele becomes fixed in the population if the simulation is tried again with a new random sampling dramatic changes in allele frequency will still occur in this second simulation the capital a allele becomes fixed in the population meaning that the lowercase a allele is lost other simulations take different paths but all lead to fixation of one allele or the other in a relatively short number of generations in contrast consider a starting population of 1,000 individuals if the population is sampled from by random mating to produce a new generation of 1,000 individuals and this process is allowed to continue for several generations genetic drift is still present but is greatly reduced compared to what was seen with the smaller population even this larger population is not immune to ultimate fixation of an allele by genetic drift however most cases a very large number of generations will pass before fixation occurs

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