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Rex Brynen (10)
Lecture

lec 12.doc

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Department
Biology (Sci)
Course Code
BIOL 469
Professor
Rex Brynen

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Description
Gregor Mendels publications paved the way for the development of the field of population genetics It has three main goals1To explain the origin and maintenance of genetic variation2To explain the patterns and organization of genetic variation3To understand the mechanisms that cause changes in allele frequencies in populationsDifferent forms of a gene are called alleles and may exist at a particular locusAt any particular locus a single individual has only some of the alleles found in the population to which it belongs The sum of all copies of all alleles at all loci found in a population makes up the gene pool which produces the phenotypic traits on which natural selection actsMost populations are genetically variableNearly all populations have genetic variation for many characters The study of the genetic basis of natural selection is difficult because genotypes alone do not uniquely determine all phenotypes Different phenotypes can be produced by a given genotype depending on the environment encountered during developmentEvolutionary change can be measured by allele and genotype frequenciesAllele frequencies are usually estimated in locally interbreeding groups within a geographic populationMendelian populationAn alleles frequency is calculated using the following formulapopulation in the alleletheof copies ofnumber Refer to ppopulation in the alleles of sumPage 491492A locally interbreeding group within a geographic population is called a Mendelian populationGenetic variation the relative proportions or frequencies of all alleles in a populationBiologists can estimate allele frequencies for a given locus by measuring numbers of alleles in a sample of individuals from a populationSum of all allele frequencies at a locus is equal to 1 so measures of allele frequency range from 0 to 1If there is only one allele at a locus its frequency1 The population is monomorphic at that locus the allele is said to be fixed The population is said to be polymorphic at a locus if there are more than one allele at that locus The frequencies of different alleles at each locus and the frequencies of different genotypes in a Mendelian population describe that populations genetic structure oAllele frequencies measure the amount of genetic variation in a population genotype frequencies show how a populations genetic variation is distributed among its members The genetic structure of a population does not change over time if certain conditions exist If an allele is not advantageous its frequency remains constant from generation to generation its frequency will not increase even if the allele is dominant A population of sexually reproducing organisms in which allele and genotype frequencies do not change from generation to generation is said to be at HardyWeinberg equilibrium Genotype frequencies can be predicted from allele frequencies Five assumptions must be made in order to meet HardyWeinberg equilibriumoMating is randomoPopulation size is very large larger the population the smaller will be the effect of genetic driftrandomchance fluctuations in allele frequenciesoThere is no migration either into or out of the populationsoThere is no mutation No change to alleles A and a and no new alleles are added to change the gene pool oNatural selection does not affect the survival of particular genotypes There is no differential survival of individuals with different genotypes
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