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The balance between the influence of natural selection and genetic drift on the population mutation rate is mainly determined by the population size. [5] Large populations are predicted to generally have lower mutation rates than smaller populations.
Tomoko Ohta also emphasized the importance of nearly neutral mutations, in particularly slightly deleterious mutations. [28] The Nearly neutral theory stems from the prediction of neutral theory that the balance between selection and genetic drift depends on effective population size. [29]
Slightly deleterious mutations are reliably purged only when their selection coefficient are greater than one divided by the effective population size. In larger populations, a higher proportion of mutations exceed this threshold for which genetic drift cannot overpower selection, leading to fewer fixation events and so slower molecular evolution.
In this theory, every evolutionary event, mutation, and gene polymorphism (neutral differences in phenotype or genotype) would have to be positively or negatively selected for and show some kind of change over many generations. [3] If these genetic differences grow between different populations speciation events can occur.
Macroevolution is guided by sorting of interspecific variation ("species selection" [2]), as opposed to sorting of intraspecific variation in microevolution. [3] Species selection may occur as (a) effect-macroevolution, where organism-level traits (aggregate traits) affect speciation and extinction rates, and (b) strict-sense species selection, where species-level traits (e.g. geographical ...
A mutation will increase genetic diversity in the short term, as a new gene is introduced to the gene pool. However, the persistence of this gene is dependent of drift and selection (see above). Most new mutations either have a neutral or negative effect on fitness, while some have a positive effect. [11]
Genetic drift, also known as random genetic drift, allelic drift or the Wright effect, [1] is the change in the frequency of an existing gene variant in a population due to random chance. [ 2 ] Genetic drift may cause gene variants to disappear completely and thereby reduce genetic variation . [ 3 ]
Population genetics is a subfield of genetics that deals with genetic differences within and among populations, and is a part of evolutionary biology.Studies in this branch of biology examine such phenomena as adaptation, speciation, and population structure.