![]() Choose that generation randomly by flipping a coin ten times and let heads be A and tails be a. ![]() In a stable population, the next generation will also have ten individuals. Imagine a population of ten individuals, half with allele A and half with allele a (the individuals are haploid). In a population of 100, that 1 individual represents only 1 percent of the overall gene pool therefore, it has much less impact on the population’s genetic structure and is unlikely to remove all copies of even a relatively rare allele. If one individual in a population of ten individuals happens to die before it leaves any offspring to the next generation, all of its genes-a tenth of the population’s gene pool-will be suddenly lost. Alleles may or may not make it into the next generation due to chance events including mortality of an individual, events affecting finding a mate, and even the events affecting which gametes end up in fertilizations. Genetic drift occurs because the alleles in an offspring generation are a random sample of the alleles in the parent generation. Drift would be completely absent in a population with infinite individuals, but, of course, no population is this large. Genetic drift is most important in small populations. Genetic DriftĪnother way a population’s allele frequencies can change is genetic drift ( Figure 11.7), which is simply the effect of chance. It should be noted that mutation is the ultimate source of genetic variation in all populations-new alleles, and, therefore, new genetic variations arise through mutation. Whether or not a mutation is beneficial or harmful is determined by whether it helps an organism survive to sexual maturity and reproduce. Beneficial mutations will spread through the population through selection, although that initial spread is slow. Harmful mutations are removed from the population by selection and will generally only be found in very low frequencies equal to the mutation rate. A mutation may produce an allele that is selected against, selected for, or selectively neutral. The change in frequency resulting from mutation is small, so its effect on evolution is small unless it interacts with one of the other factors, such as selection. A mutation can change one allele into another, but the net effect is a change in frequency. Mutation is a change in the DNA sequence of the gene. Mutation is a source of new alleles in a population. Over time, the allele will increase in frequency in the population. If conditions remain the same, those offspring, which are carrying the same allele, will also benefit. If it is an advantage, then that individual will likely have more offspring than individuals with the other phenotypes, and this will mean that the allele behind the phenotype will have greater representation in the next generation. Depending on the environmental conditions, the phenotype confers an advantage or disadvantage to the individual with the phenotype relative to the other phenotypes in the population. Natural selection has already been discussed. In fact, we know they are probably always affecting populations. ![]() Those factors are natural selection, mutation, genetic drift, and migration (gene flow). The Hardy-Weinberg equilibrium principle says that allele frequencies in a population will remain constant in the absence of the four factors that could change them. Explain how each evolutionary force can influence the allele frequencies of a population.Describe the four basic causes of evolution: natural selection, mutation, genetic drift, and gene flow.Gene Flow.Learning Objectives By the end of this section, you will be able to: Populations, species, and conservation genetics. University of California Museum of Paleontology (UCMP). Proceedings of the Royal Society B: Biological Sciences, 282(1820), 20152189. On the origin of mongrels: Evolutionary history of free-breeding dogs in Eurasia. Annual Review of Ecology and Systematics, 167–188. Philosophical Transactions of the Royal Society of London. Effects of life history traits on genetic diversity in plant species. Unprecedented low levels of genetic variation and inbreeding depression in an island population of the black-footed rock-wallaby. Accessed on 9 July, 2020 from Ĭhoudhuri, S.
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