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Encyclopedia > Selective sweep

A selective sweep is the reduction or elimination of variation among the nucleotides in neighbouring DNA of a mutation as the result of recent and strong natural selection. The gene pool of a species or a population is the complete set of unique alleles that would be found by inspecting the genetic material of every living member of that species or population. ... A nucleotide is a chemical compound that consists of a heterocyclic base, a sugar, and one or more phosphate groups. ... The general structure of a section of DNA Deoxyribonucleic acid (DNA) is a nucleic acid —usually in the form of a double helix— that contains the genetic instructions specifying the biological development of all cellular forms of life, and most viruses. ... In biology, mutations are changes to the genetic material (usually DNA or RNA). ... Natural selection is the process by which individual organisms with favorable traits are more likely to survive and reproduce. ...


A selective sweep can occur when a new mutation occurs in a gene that increases the fitness of the carrier. Natural selection will favour those that have a higher fitness, with as a result that the new mutation will increase in frequency in the populations. As its prevalence increases, the neutral and even slightly deleterious genetic variation linked to the new mutation will also become more prevalent. This phenomenon is called genetic hitchhiking. A strong selective sweep results in a region of the genome where the positively selected haplotype (the allele and its neighbours) are essentially the only ones that exist in the population, resulting in a large reduction of the total genetic variation at that locus. Fitness in biology refers to individuals ability to propagate its genes. ... The process by which an evolutionary neutral or in some cases deleterious allele or mutation may spread through the gene pool by virtue of being linked to a beneficial mutation. ... A haplotype, a contraction of the phrase haploid genotype, is the genetic constitution of an individual chromosome. ...


Whether a selective sweep has occurred or not can be investigated by measuring linkage disequilibrium, i.e., whether a given haplotype is overrepresented in the population. Normally, genetic recombination will result in the reshuffling of the different alleles within a haplotype, and none of the haplotypes will dominate the population. However, during a selective sweep, selection for a specific haplotype will also result in selection of neighbouring alleles. Therefore, the presence of strong linkage disequilibrium might indicate that there has been a 'recent' selective sweep, and can be used to identify sites recently under selection. Linkage disequilibrium (LD) is the non-random association of alleles at two or more loci on a chromosome. ... Genetic recombination is the transmission-genetic process by which the combinations of alleles observed at different loci (plural of locus) in two parental individuals become shuffled in offspring individuals. ...


 
 

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