fixation probability
Patwa Z & Wahl LM 2008 The fixation probability of beneficial mutations. J R Soc Interface 5:1279-1289.
- Lambert pointed out that the factor 2 in Haldane's result of π ≈ 2s for very small s stems from the assumption that the offspring distribution is Poisson
- for near-critical branching processes, more generally, π ≈ 2s / σ, where σ is the variance of the offspring distribution
- increased reproductive variance always reduces the fixation probability in such models
- in typical models of population genetics, it is assumed that mutations are rare events, such that an invading mutant strain will not mutate again before fixation or extinction occurs
- in quasi-species models, the offspring of a mutated individual are very likely to mutate before fixation
- the fitness of an invading quasi-species is not solely determined by the fitness of the initial/parent mutant, but depends on the average fitness of the 'cloud' of offspring mutants related to that parent, continually introduced by mutation, and removed through selection
- the fixation of a mutant is defined to be its establishment as a common ancestor of the whole population
- since the population is never genetically identical, the standard definition does not apply
