Coalescent Theory
Coalescent theory refers to a retrospective model in genetics of population genetics. This model attempts to locate all the alleles of gene that is shared by the members of the population to one ancestral copy called the most recent common ancestor. In some cases it is also known as the co-ancestor in emphasizing coalescent relationship.
Gene genealogy is a typical representation of inheritance relationships that alleles have. It is similar in its form to phylogenetic tree. Gene genealogy is called coalescent. The basis of the coalescent theory lies in understanding statistical properties that coalescent has under varying assumptions forms.
Coalescent runs the models of the genetic drift in a backward manner in time so as to investigate antecedents’ genealogy. In a simplest case, the coalescent theory does not assume recombination, gene flow, population structure, or natural selection. However, advances in the coalescent theory allow extension to the basic coalescent.
It can also include selection, recombination and almost any demographic model or arbitrary complicated evolutionary in the analysis of population genetic. Coalescent mathematical theory was developed originally by John Kingman at the beginning of the 1980s.
One aspect of modern evolutionary theory synthesis entails population biology and genetics to some levels. Considering the fact that evolution is usually measured using units in a population and that only populations are capable of evolving rather than individuals, population genetics and population biology are an intricate part of evolution theory via natural selection.
First, Charles Darwin published his natural selection and evolution ideas. At this time, genetics were yet to be discovered. Since tracing genetics and alleles is crucial in population genetics and population biology, Darwin was not able to cover the ideas fully in his work. Today, advancement in technology and the expansive knowledge in genetics and biology more on population genetics and population biology can be incorporated in the evolution theory.
Just like the Hardy-Weinberg Equilibrium, Coalescent theory has some assumptions that rid changes in the alleles via chance events. Coalescent theory assumes the absence of genetic drift of the alleles out or into a population. The theory assumes that natural selection is not at work in the population over time.
If any of these assumptions is true, then it is possible to find most recent common ancestor among two distinct lineages of the same species. In addition, if any of these assumptions are true, then there are many obstacles that must be overcome before pinpointing most recent common ancestor for the species.
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Sources
http://en.wikipedia.org/wiki/Coalescent_theory
http://sysbio.oxfordjournals.org/content/58/1/162.full
http://evolution.about.com/od/Terms-A-G/a/The-Coalescent-Theory.htm