Chapter 23 - Population Evolution

Chapter 23 - Population Evolution - EVOLUTION OF...

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Knight/Evolution of Populations 1 E VOLUTION OF P OPULATIONS (23) Population Genetics Synthesizes Darwinian evolution and Mendelian genetics Variation exists in a population; variations are caused by alleles. Alleles are inheritable. Population : interbreeding group of organisms belonging to the same species. Species: (biological) Population whose members have the potential to interbreed with one another in nature and produce viable (fertile) offspring. Free breeding amongst themselves, but not other species. Not reproductively isolated from other members, only other species. Subspecies : morphologically distinct species that don’t interbreed with main group. Populations are “defined” by their total number of genes. All the alleles of all the genes in a population are given the term Gene Pool. From one generation to another the frequency of certain alleles may increase/decrease. Favorable alleles more likely to increase; unfavorable decrease. Changes in the allele frequency accumulate in the gene pool. The gene pool changes slowly over time. Microevolution is the change in the gene pool (allele frequency within population) over a period of time (generations). This can be observable if the lifespan of an organism is short. (ie. Bacteria, viruses) What can cause a change in the relative frequency of alleles? A. Emigration or immigration: flow of gene into/out of a population. [Gene flow] B. Mutation : allele R mutates to r. Frequency of r will increase.
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Knight/Evolution of Populations 2 C. Small population: reproduction within a small subset of larger population. Decrease in population size caused by small surviving group ( ) or small group breaking off from main population to inhabit new area ( ) Small population generally not representative of the larger population. Chance can change allele frequency. D. Natural Selection: difference in reproductive/survival rates. E. Non random mating: decreases number of heterozygotes and increases the number of homozygotes. How can we measure a change in the frequency of alleles within a population? Determine a standard by which to compare the population to. If a population deviates from the standard, then identify the magnitude and direction of the change. Given the magnitude and the direction, determine which forces are at work to cause the change. Standard- Hardy-Weinberg Equilibrium States that frequency of alleles in a gene pool will remain constant unless acted on by some outside force (like A – E). Populations in H-W equilibrium are not evolving and are not acted upon by these outside forces. H OW LIKELY IS T HIS ? Allows you to calculate frequencies of alleles in a gene pool if we know the genotypes and to calculate the frequencies of genotypes if we know the frequencies of alleles.
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Knight/Evolution of Populations 3 p 2 + 2pq + q 2 = 1 (frequency of genotypes must add up to 1) p + q = 1 (frequency of both alleles must add up to 1) p = frequency of allele A
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This note was uploaded on 02/14/2012 for the course BIO 151 taught by Professor Grinblat during the Fall '08 term at University of Wisconsin.

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Chapter 23 - Population Evolution - EVOLUTION OF...

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