Thursday, October 4, 2012

What Causes Evolutionary(genetic) Change

Deviation from the proportions of gene frequencies and genotype frequencies as defined by Hardy-Weinberg law of equilibrium is explained by one or more of the four forces of evolution,mutation,natural selection,genetic drift and gene flow.These forces result in genetic change over time.

Mutations are DNA coding errors that are biochemically manifested as permanent changes in the structure or amount of genetic material within cells.Mutations are the only source of new genetic material.

Although a mutation can occur in any cell only mutations in gametes have implications for offspring and therefore they have greater importance for evolution then do mutations in somatic cells.

Natural selection begins with variation among the individual members of a population.Members with advantageous characteristics survive and reproduce in greater number than do the members lacking the same characteristics.Allele frequencies can increase,decrease or remain the same owing to natural selection.

Advantageous characteristics can be visible physical attributes,invisible biochemical attributes or some combination of the physical and the biochemical.

Genetic drift is change in gene frequency due to chance.Within smaller populations chances are greater that gene frequencies  will change randomly.Drift was likely an important force in most human evolution since prior to 10,000 year.

Gene flow is the transfer of genes across population boundaries .In humans gene flow  became a major force of evolution mostly within the last 10,000 years when population size increased and created greater opportunities for contact and reproduction.

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