Genetic variation is the basis for evolution. This effect on gene frequencies is known as the founder effect. A new population is started by a small group of members of the original population and by chance, a previously rare allele may be relatively frequent. Sometimes, a population may become fragmented into smaller populations due to urban development or other events. Such a reduction of genetic diversity is called a genetic bottleneck. The resulting composition of the gene pool was selected randomly (i.e., surviving the disturbance was not determined by the genetic make-up of the individual). A major disturbance, such as a natural disaster, may drastically reduce population size and thereby diminish genetic variation. In genetic drift, chance events alter the allele frequencies of a population. Juvenile male baboons almost always leave their birth troops, likely to avoid inbreeding, and join a new troop, where they may pass their genes to offspring. Female baboons mate most frequently with dominant males in a troop. A classic example of gene flow is observed in most baboon species. In this case, alleles for the traits that are selected against will become less frequent in the population.įurthermore, populations can experience gene flow, the transfer of alleles into and out of gene pools, due to migration. Individuals in natural populations may also select their mates based on certain characteristics, and thus do not reproduce randomly. Therefore, such harmful mutations are likely to be eliminated by natural selection. However, if a mutation reduces the chances of survival, the organism may die before reproducing. Most mutations do not cause significant changes to the health or functioning of an organism. Mutations create new alleles and increase genetic variability. The original sources of genetic variation are mutations, which are changes in the nucleotide sequence of DNA. Conditions that change the genetic variability of a population include mutations, natural selection, non-random mating, gene flow, and genetic drift (small population size). Therefore, any deviations from the five conditions of Hardy-Weinberg equilibrium can alter the genetic variation of a given population. In a population that is not at Hardy-Weinberg equilibrium, the frequency of alleles changes over time.
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