The original source of new alleles, upon which selection...

The original source of new alleles, upon which selection operates, is mutation, a random event that occurs without regard to selectional value in the organism. Although many model organisms have been used to study mutational events in populations, some investigators have developed abiotic molecular models. Soll et al. (2006. Genetics 175:267-275) examined one such model to study the relationship between both deleterious and advantageous mutations and population size in a ligase molecule composed of RNA (a ribozyme). Soll found that the smaller the population of molecules, the more likely it was that not only deleterious mutations but also advantageous mutations would disappear. Why would population size influence the survival of both types of mutations (deleterious and advantageous) in populations?

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Key Concepts

Population Size

Population size plays a critical role in evolutionary dynamics. In small populations, the impact of genetic drift is magnified, leading to a higher probability that both beneficial and deleterious mutations will be randomly lost, in contrast to larger populations where natural selection has a stronger, more consistent influence.

Natural Selection

Natural selection is the process by which advantageous traits become more common while deleterious traits are removed from a population over time. However, its effectiveness can be diminished in small populations where the randomness introduced by genetic drift can override the selective advantages of beneficial mutations.

Mutation

Mutations are random changes in the genetic material that introduce new alleles into a population. They serve as the fundamental source of genetic variation, providing both beneficial and harmful changes, and occur without any inherent bias toward improving organismal fitness.

Genetic Drift

Genetic drift refers to random fluctuations in allele frequencies that occur by chance, particularly in small populations. Because of these random events, even advantageous mutations can be lost and deleterious mutations may persist, affecting the survival of mutations independently of their impact on fitness.

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