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Chapter 17

BI111 Chapter 17 - Microevolution.docx

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Tristan Long

BI111 Chapter 17Microevolution Genetic Changes within Populatioins MicroevolutionSmall scale heritable change in the genetics of a populationhave side to be taken place when allele frequencies experience a shift Eg Evolution of antibiotic resistance in bacteria PopulationAll individuals of a single species that live together at the same place and time Natural Selection acted uponIn some species individuals appear very differently but in most cases appear alike Phenotypic VariationDifferences in appearance or function passed through generations Qualitative Variationexist in two or more discrete states and intermediate forms are absent Eg Snow geese have either blue or white feathersMendel studied Quantitative Variationindividuals differ in small incremental waysA broad low curve indicates a lot of variation among individualsA high narrow little Polymorphismthe existence of discrete variants in a character such traits are polymorphic Eg Human blood type A B O are polymorphicPhenotypic variation caused by environment therefore genetic and phenotypic variations may not correlateonly genetically based variation is subject to evolutionary change Genetic Variationmade by two sources1 Production of new allelesMutations in DNA 2 Rearrangement of existing allelesGenetic recombination 60010 10combinations of alleles possible in humans but only 10 exist today Diploid organismspairs of homologous chromosomesgenotype includes 2 alleles at every locus Gene PoolSum of alleles at all gene loci in all individuals in the population Genotype Frequenciesthe percentages of individuals processing each genotype Allele Frequenciesthe relative abundance of the different alleles Null modelsconceptual models which predict what would happen if a factor had no effecttheoretical reference points against which observations can be evaluated HardyWeinberg Principlecondition which population of diploid organisms achieves geneticequilibrium neither allele nor genotype frequencies change in succeedinggenerationsIf conditions are met 1 No Immigration or Emigration2 Large Population3 Random Mating4 Individuals produce successful offsprings throughout generations5 No Mutations occurringTherefore It proves that dominant alleles does not replace recessive alleles Agents of Microevolutionary Change Mutationa heritable change in DNAintroduces new genetic variation into population
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