EvolutionMechanisms101

EvolutionMechanisms101 - Evolutionary Mechanisms - 1 The...

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Evolutionary Mechanisms - 1 The Gene Pool and Genetic Equilibrium As we stated at the beginning of our discussion on evolutionary principles, evolution involves changes that occur in the frequency of a gene's alleles in a population from generation to generation. Each individual member of a population inherits a set of genes. He or she can not evolve or change the alleles inherited. But the contribution he or she makes to the population's gene pool through reproduction, relative to the contribution other members of the population make, can change the population's genetic composition from generation to generation. The collection of genes in a population is called the gene pool. For a population's gene pool to change, there must be some mechanism that promotes differential reproduction (or differential survival that is reflected in reproduction. When such change occurs, we have evolution. A review of the inheritance of a single gene illustrates this. In a population of cats, there are two pre-existing alleles for coat color: black and white. Black is dominant. The two coat colors have been reproduced year after year. Then one year, a new nocturnal predator happens into the environment. This predator sees the white cats at night and eats them. The white cats rarely reproduce, since they are eaten when young and have fewer predator defenses. Within a few generations, the frequency of the white allele diminishes significantly. The predator has been the selection force behind the change in allele frequency for cat coat color. Initial Frequency of coat color alleles We can see this and explain this today, because we know how genes and alleles are inherited. In the 1800's, they did not know this, and for about 50 years after Darwin's publications, scientists and others searched for mechanisms of evolution. In the early 1900’s Mendel’s work was rediscovered by a number of researchers, who, at first, tried to use genetics to disprove Darwin’s theory of gradual evolution through slow selection of beneficial characteristics. The “Mendel” group promoted the idea that changes would occur rapidly via mutations, and that natural selection had no role in changes that occurred in populations through time. It took many years to bring together genetics, population biology and natural selection as means of evolution. It stated at a conference in 1908.
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Evolutionary Mechanisms - 2 The HARDY-WEINBERG principle for genetic equilibrium Hardy and Weinberg demonstrated that the equation for a binomial expansion (p 2 + 2 pq + q 2 = 1) could be used to calculate gene frequencies within a population. They first showed the gene frequency for genetic equilibrium, the condition in which gene frequency would not change from generation to generation. Genetic Equilibrium Formula
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This note was uploaded on 02/27/2009 for the course SC 424111 taught by Professor Various during the Summer '09 term at Bentley.

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EvolutionMechanisms101 - Evolutionary Mechanisms - 1 The...

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