g640Selection

g640Selection - selection Adaptation alleles that enhance...

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Unformatted text preview: selection Adaptation alleles that enhance survival and reproduction increase gradually in frequency population becomes progressively better able to survive and reproduce in the environment Adaptation EVOLUTIONARY ADAPTATION - progressive genetic improvement - increase in frequency through time of individuals superior in survival and reproduction- due to inherited differences in the ability of the organism to survive and reproduce Selection Unit of selection = individual- not species- not subpopulation- not sibship Models of selection Deterministic- infinite population size- no mutation- random mating (no migration)- discrete vs continuous generations- diploid vs haploid haploid model competing genotypes with different rates of potential increase haploid model Initially use a discrete generation model- fitness based on viability alone- absolute fitness = - probability of genotype survivorship- relative fitness = - fitness expressed relative to a particular genotype - (arbitrarily set = 1.0) haploid model Change in allele frequency p (w A ) . p = ----------------------- . p (w A ) + q (w a ) p (w A ) 0.5 (1) p = ---------------------- = ----------------------- = 0.6 p (w A ) + q (w a ) 0.5 (1) + 0.5 (0.67) haploid model Since we are using an arbitrary best fitness for allele A [o] , (w A ) = 1- we can express change in terms of a selection coefficient against allele a- s = 1 - (w a ) p 0.5 . p = ------------- = ---------------- . 1 - qs 1 - (0.5)(0.33) haploid model Change in allele frequency p (w A ) . p = ----------------------- . p (w A ) + q (w a ) we can also express the average fitness of the population as :- w = p (w A ) + q (w a ) _ haploid model We can predict the future frequency of the alleles as : p . p t = ---------------- . p + q (1 s) t haploid model We can estimate the selection coefficient from information on allele frequencies in successive generations? If s is small (actually can be just < 0.2)- p t p . ln [ ---- ] = ln [ ---- ] + s t . q t q haploid model We can estimate the selection coefficient from information on allele frequencies in successive generations? If s is small (actually can be just < 0.2)- p t p . ln [ ---- ] = ln [ ---- ] + s t . q t q Use slope to estimate s haploid model estimating the selection coefficient from allele frequency changes?- Consider two competing bacterial strains which differ at just one locus Slope = selection coefficient Selective changes in populations Example:- antibiotic resistance in bacteria- antibiotic resistant allele has higher fitness in presence of antibiotics Penicillin resistant Streptococcus pneumoniae diploid model We usually use a discrete generation model - viability selection- absolute fitness = - probability of genotype survivorship- relative fitness = - fitness expressed relative to a particular genotype (arbitrarily set = 1.0) Where does selection act in...
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This note was uploaded on 07/17/2008 for the course EEOB 640 taught by Professor Fuerst during the Spring '05 term at Ohio State.

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g640Selection - selection Adaptation alleles that enhance...

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