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THE EVOLUTION OF POPULATIONS CHAPTER 23 POPULATIONS Localized group of individuals belonging to the same species Species – group of individuals who have the potential to interbreed and produce fertile offspring Similarities in individuals are o Morphological – structural o Physiological – metabolic activities o Behavioral – similar responses to same stimuli Gene Pool Total aggregate of genes in a population at any one time Nearly all genes in available pool have two or more slightly different molecular forms – alleles In closed population, only mutation brings about changes to the gene pool Genetic Variation Difference in genes or other DNA segments among individuals of the same population Genotype is inherited Phenotype is the environmental influence on genotype Average heterozygosity – average percent of loci that are heterozygous; measure of the relative age of a specific population Variation between populations often due to geographic variations Genetic Variation Sources of variation o Formation of new alleles through mutation o Altering of gene number and position due to errors in meiosis o Rapid reproduction rate increases potential for variation o Sexual reproduction shuffles genes more effectively than asexual Hardy Weinberg Equilibrium Idea that allele frequency is constant from generation to generation Used to assess whether a population is evolving at a specific locus by determining what the population would be like if it were NOT evolving at that locus Scenario created is compared to actual population; no change – no evolution; change – evolution is occurring Hardy Weinberg Equilibrium All 5 conditions must be met for there to be no evolution occurring: 1. No mutations 2. Random mating 3. No natural selection 4. Extremely large population size 5. No gene flow Altering Allele Frequencies in a Population Natural Selection – only mechanism that consistently causes adaptive evolution Genetic Drift – chance events that change allele frequencies Gene Flow – transfer of alleles into or out of a population
