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Coalescent theory is a model of how alleles sampled from a population may have originated from a common ancestor. In the simplest case, coalescent theory assumes no recombination , no natural selection , and no gene flow or population structure , meaning that each variant is equally likely to have been passed from one generation to the next.
Sir John Frank Charles Kingman FRS [4] (born 28 August 1939) [5] is a British mathematician. [2] [6] He served as N. M. Rothschild and Sons Professor of Mathematical Sciences and Director of the Isaac Newton Institute at the University of Cambridge from 2001 until 2006, [1] [5] [7] when he was succeeded by David Wallace.
In 1908, G. H. Hardy and Wilhelm Weinberg modeled an idealised population to demonstrate that in the absence of selection, migration, random genetic drift, allele frequencies stay constant over time, and that in the presence of random mating, genotype frequencies are related to allele frequencies according to a binomial square principle called the Hardy-Weinberg law.
Coalescent theory relates genetic diversity in a sample to demographic history of the population from which it was taken. It normally assumes neutrality , and so sequences from more neutrally evolving portions of genomes are therefore selected for such analyses.
The allele frequency spectrum can be written as the vector = (,,,,), where is the number of observed sites with derived allele frequency .In this example, the observed allele frequency spectrum is (,,,,), due to four instances of a single observed derived allele at a particular SNP loci, two instances of two derived alleles, and so on.
Another important branch of population genetics that led to the extensive development of coalescent theory is phylogenetics. Phylogenetics is an area that deals with the reconstruction and analysis of phylogenetic (evolutionary) trees and networks based on inherited characteristics [ 45 ] Traditional population genetic models deal with alleles ...
Coalescent theory – Model for tracing the history of genetic variation; Variation Genetic variation – Difference in DNA among individuals or populations Genetic diversity – Total number of genetic characteristics in a species; Gene frequency – The relative frequency of a variant of a gene at a particular locus in a population
Under conditions of genetic drift alone, every finite set of genes or alleles has a "coalescent point" at which all descendants converge to a single ancestor (i.e. they 'coalesce'). This fact can be used to derive the rate of gene fixation of a neutral allele (that is, one not under any form of selection) for a population of varying size ...