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Published byAustin O’Connor’ Modified over 9 years ago
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Hardy-Weinberg equilibrium if p = frequency of allele A q = frequency of allele a p + q = 1, ( p + q ) 2 = 1 p 2 + 2pq + q 2 = 1 if only law of probability affects the frequency w/ which gametes combine to form new individuals
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Bisexual population Large population Random mating No mutation Migration ~ 0 Natural selection does not affect the locus
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A population that is in Hardy-Weinberg equilibrium will experience no change in either genotype frequency or allele frequency If one or more of the conditions is violated, genotype frequency and allele frequency will change
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Example If only 6% of the population displays pale eyes (recessive gene e). What is the frequency of genotype Ee in this population? q 2 = 0.06 ---> q = 0.24 p + q = 1 ---> p = 0.76 Ee = 2pq = 2(0.76)(0.24) = 0.36
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Genetic variation Cline – a measurable, gradual change over a geographical region in the average of some phenotype character Ecotype – abrupt changes in the phenotype characters within a species, which often reflect abrupt changes in local environment
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Geographic isolates – semi-isolated populations prevented by some extrinsic barriers from a free flow of genes Genetic polymorphism – the existence within a species or population of different forms of individuals
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Maintenance of balanced polymorphism (vs. transitional or directional polymorphism) heterosis diversifying evolution frequency-dependent selection selective forces operating in different directions within different patches of a fine mosaic in the population
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Stabilizing, directional, diversifying or disruptive evolution Speciation Allopatric speciation Sympatric speciation
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Isolation mechanism Pre-zygotic: habitat, temporal, ethological, mechanical Post-zygotic hybrid inviability or weakness hybrid sterility F 2 breakdown
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Reduction in variation inbreeding, bottlenecks, founder effect, genetic drift genetic drift - random shifts in allele frequencies
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Effect of small populations More demographic variation, inbreeding depression, genetic drift → higher risk of extinction Minimum viable population size the threshold # of individuals that will ensure the persistence of subpopulation in a viable state for a given time interval
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Effective population size (Ne) the size of a genetically idealized population with which an actual population can be equated genetically, Ne = N, if equal sex ratio equal probability of mating constant dispersal rate progeny per family randomly distributed
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unequal sex ratio Ne = 4 Nm˙Nf / (Nm + Nf ) population fluctuation 1 / Ne = (1 / t )(1/N 1 + 1/N 2 + … + 1/N t ) non-random progeny distribution N k Ne = ----------------------------------------- (N/N-1)˙V k /k˙(1+F) + (1-F)
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Effect of continental drift Distribution/radiation of monotremes and marsupials
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Extinction and its causes Natural causes: climatic changes and stochastic event Human disturbance habitat alteration over-exploitation exotic species diseases and other factors
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