Chapter 19 Evolutionary Genetics

Chapter 19 Evolutionary Genetics - Evolutionary Genetics...

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Evolutionary Genetics Suggested problems: 12, 14, 16
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Darwin’s theory of evolution, 1859 species change over time—this is called evolution (this idea pre-dates Darwin) Darwin suggested a mechanism by which species evolve: via natural selection contrast with artificial selection : humans choosing certain characteristics over others through many generations of breeding in agricultural plants, dogs, cattle, etc. natural selection: Principle of variation: there is variation within individuals in a species Principle of selection: - certain characteristics cause individuals to be more “fit” for survival and reproduction -more “fit” individuals will contribute more offspring to the next generation than less fit individuals (or, in a competition for survival among individuals, more “fit” individuals will predominate) Principle of heredity: offspring tend to resemble their parents; the characteristics that cause individuals to be more “fit” are heritable
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The same forces that change allele frequencies in populations are involved in evolution of populations -forces that increase/maintain allele variation in a population prevent populations from diverging (migration, mutation, balanced polymophisms) -forces that decrease allele diversity cause populations to diverge (inbreeding, genetic drift, directional selection)
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Adaptive Landscapes: topographic depiction of low and high “fitness” -may include just one “peak” representing directional selection of a single allele -may have more than one peak from multiple ways to get a high level of “fitness” example: two loci influence a character, intermediate phenotypes are most fit AB/ab, Ab/Ab, and aB/aB are all fit AB/AB and ab/ab are less fit frequencies of A and a, B and b can change, but one allele tends to become fixed in a population, therefore the fitness peaks are Ab/Ab an aB/aB
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Adaptive Landscapes -different populations may take different routes to fitness -different fitness peaks are not necessarily of the same height (may not denote the same level of fitness), but choice is incremental , so populations can become fixed at peaks that are not the highest -sometimes the force of selection is not great enough to counteract genetic drift, and populations become fixed at fitness valleys
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Speciation evolutionary genetics definition of species: group of interbreeding organisms
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This note was uploaded on 05/28/2011 for the course BIO 220 taught by Professor Dr.leatherman during the Spring '10 term at N. Colorado.

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Chapter 19 Evolutionary Genetics - Evolutionary Genetics...

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