Fixation And Genetic Equation

One result of random genetic drift and gene substitution is mutant alleles, however the probability that these mutations become fixed in a population is not solely dependent on the advantageous nature of the allele, rather the probability of fixation is determined by the allele frequency, the selective advantage or disadvantage, and the effective population size. The probability of fixation for a particular allele is demonstrated by the equation where probability is equal to 1 minus the exponential of (-4Nesq) divided by (1-e-4Nes). In this equation, q represents the initial frequency of the allele and s is the selective advantage or disadvantage. Mathematically, the fixation probability of a neutral allele is equal to its frequency. This is because …show more content…
The average number of generations needed to fix or lose an allele becomes significantly shorter as the allele frequency approaches either extreme, 1 or 0. When the population size is N, neutral mutation fixation time t is equal to 4N generations and a mutation with a selective advantage of s takes (2/s)ln(2N) generations to become fixed. For a mutant with a selective disadvantage, there is a low fixation probability, which means that if the mutant is to become fixed the fixation time must be much faster than neutral mutant. Selective advantage mutants behave similar to adverse mutations because the mutation is either quickly lost or quickly fixed. Additionally, the number of mutants fixed per generation is described by the rate of gene substitution. Numerically, the rate of substitution is equal to the total number of mutations multiplied by the probability of fixation. For a neutral mutation, the rate of substitution is independent of population size, however for alleles with genic selection the rate of substitution is population size dependent. The inverse of the rate of gene substitution is also equal to the average time between the fixation of two consecutive