Background
Different genetic variants within a species are referred to as alleles, and so a new mutation is said to create a new allele. In population genetics, each allele is characterized by a selection coefficient, which measures the expected change in an alleles frequency over time. The selection coefficient can either be negative, corresponding to an expected decrease, positive, corresponding to an expected increase, or zero, corresponding to no expected change. The distribution of fitness effects of new mutations is an important parameter in population genetics and has been the subject of extensive investigation Although measurements of this distribution have been inconsistent in the past, it is now generally thought that the majority of mutations are mildly deleterious, that many are have little effect on an organisms fitness, and that a few can be favorable. As a result of natural selection, unfavorable mutations will typically be eliminated from a population while favorable changes are quickly fixed, and neutral changes accumulate at the rate they are created by mutations.
Read more about this topic: Mutation Rate
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