Lecture #10 Chapter 23~ The Evolution of Populations.

Download Lecture #10 Chapter 23~ The Evolution of Populations.

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  • Lecture #10Chapter 23~ The Evolution of Populations

  • Population geneticsPopulation: a localized group of individuals belonging to the same speciesSpecies: a group of populations whose individuals have the potential to interbreed and produce fertile offspringGene pool: the total aggregate of genes in a population at any one timePopulation genetics: the study of genetic changes in populationsModern synthesis/neo-DarwinismIndividuals are selected, but populations evolve.

  • Hardy-Weinberg TheoremServes as a model for the genetic structure of a nonevolving population (equilibrium)5 conditions:1- Very large population size;2- No migration;3- No net mutations;4- Random mating;5- No natural selection

  • Hardy-Weinberg Equationp=frequency of one allele (A); q=frequency of the other allele (a); p+q=1.0 (p=1-q & q=1-p)P2=frequency of AA genotype; 2pq=frequency of Aa plus aA genotype; q2=frequency of aa genotype; p2 + 2pq + q2 = 1.0

  • Microevolution, IA change in the gene pool of a population over a succession of generations1- Genetic drift: changes in the gene pool of a small population due to chance (usually reduces genetic variability)

  • Microevolution, IIFounder Effect: a cause of genetic drift attributable to colonization by a limited number of individuals from a parent population (island populations)Inherited diseases

  • Microevolution, IIIThe Bottleneck Effect: type of genetic drift resulting from a reduction in population (natural disaster) such that the surviving population is no longer genetically representative of the original population

  • Microevolution, IV5- Natural Selection: differential success in reproduction; only form of microevolution that adapts a population to its environment

  • Microevolution, V2- Gene Flow: genetic exchange due to the migration of fertile individuals or gametes between populations (reduces differences between populations)

  • Microevolution, VI3- Mutations: a change in an organisms DNA (gametes; many generations); original source of genetic variation (raw material for natural selection)Can be reversibleMost not beneficialIt does not change populations, genetic drift and natural selection do

  • Microevolution, VII4- Nonrandom mating (selective breeding): inbreeding and assortive mating (both shift frequencies of different genotypes)

  • Population variationPolymorphism: coexistence of 2 or more distinct forms of individuals (morphs) within the same populationGeographical variation: differences in genetic structure between populations due to environment (cline)

  • ReviewDarwins observations/inferencesEvidence of evolutionHardy-Weinberg requirementsHardy-Weinberg equations/problemsFactors that cause evolution

  • TodayCause of variationAltering allelic frequenciesNatural selection in depthPreservation of genetic variation - necessary

  • HomeworkCh. 25 reading guide due tomorrow

  • VariationMutation and Sexual RecombinationHIV1010 new viruses/dayRNA higher mutation rateMutations in every gene each dayDrug cocktailsReinfections

  • 3 main causes of allelic changesGene flow random, may not be beneficial, reduces differences between populationsGenetic Drift random, may not be beneficialNatural selection interacts with environment, creates organisms that better interact with their environment (adaptive evolution)

  • Lets Focus on Natural selectionFitness: contribution an individual makes to the gene pool of the next generationIt is a little more complicated than that (less fit genes can hitchhike with a fit gene)Relative fitness: how an individual contributes to the next generation (sterile individuals have a relative fitness of 0

  • Modes of natural selection3 types:A. DirectionalB. DiversifyingC. Stabilizing


  • Stabilizing Selection

  • Sexual selectionCreates Sexual dimorphism: secondary sex characteristic distinctionSexual selection: selection towards secondary sex characteristics that leads to sexual dimorphismIntrasexual males competing (alpha male)Intersexual females choosing

  • Variation preservationPrevention of natural selections reduction of variationDiploidy 2nd set of chromosomes hides variation in the heterozygoteBalanced polymorphism 1- heterozygote advantage (hybrid vigor; i.e., malaria/sickle-cell anemia); 2- frequency dependent selection (survival & reproduction of any 1 morph declines if it becomes too common; i.e., parasite/host)

  • Population Genetics Lab