Chapter 23: The Evolution of Populations

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Chapter 23: The Evolution of Populations. Population Genetics. microevolution change in genetic makeup of a population from generation to generation. macroevolution evolutionary change above the species level. - PowerPoint PPT Presentation


  • Chapter 23:The Evolution of Populations

  • Population Genetics

    microevolution change in genetic makeup of a population from generation to generation

  • macroevolution evolutionary change above the species level

  • population group of individuals of the same species living in the same area

  • gene pool all the genes in a given population at a given time

  • allele frequency proportion of an allele in a gene pool

    p = dominant alleleq = recessive allele

    f (p) = frequency of the dominant allelef (q) = frequency of the recessive allele

  • Calculating allele frequency:

  • Genotype# of IndividualsGenotypic frequenciesMM1787MM = 1787/6129 = 29%MN3039MN = 3039/6129 = 50%NN1303NN = 1303/6129 = 21%Total6129

  • Hardy-Weinberg Theoremhelps measure changes in allele frequencies over timeprovides an ideal population to use as a basis of comparison

  • Conditions for Hardy-Weinberg Equilibrium:

    Large populationNo gene flowNo mutationsRandom matingNo natural selection hypothetical population that is not evolving rarely met in nature

  • Mutation and sexual recombination only sources of new variations

    mutation changes in nucleotide sequence in DNA

  • point mutations change in one nucleotide

  • gene duplication duplication of a chromosome segment

  • sexual recombination crossing over, shuffling of genes during meiosis

  • Genetic Drift change in allele frequencies due to chanceusually in smaller populationsreduces genetic variation

  • bottleneck effect when a population has been dramatically reduced, and the gene pool is no longer reflective of the original populations

  • Human actions can create a genetic bottleneck

  • founder effect when a small number of individuals colonize a new area; new gene pool not reflective of original population

  • The Fugate family Kentucky's Troublesome Creek

  • gene flow when a population gains or loses alleles

    a movement of fertile individuals leaving/arriving a reduces differences between populations

  • genetic variation heritable variations in a population

  • discrete characteristics are all one discrete variety

  • quantitative characteristics vary along a continuum, usually due to influence of two or more genes

  • average heterozygosity measure of polymorphism in a population

  • geographic variation difference in variation between population subgroups in different areas

  • cline a graded change in a trait along a geographic axis

  • Evolutionary Fitness

    fitness contribution an individual makes to the gene pool of the next generation, relative to the contributions of other individuals

    (the more offspring that you have that survive = more fit you are)

  • relative fitness fitness of a particular genotype

  • Types of selectiondirectional selection shift toward a favorable variation

  • disruptive selection favors the extremes

  • stabilizing selection favors the mean

  • Heterozygous Advantage when individuals heterozygous Recessive allele is maintained in the population

  • Example: sickle-cell anemia

    prevelence of malaria sickle-cell disease

  • Sexual selection a natural selection for mating success

  • Sexual dimorphism differences between the sexes in secondary sexual characteristics

  • Not necessarily better adaptations; example mane on lion very hot, feathers on peacock very expensive to make

  • Common misconceptions:Natural selection acts on phenotype, not genotype!

    Natural selection does not create more perfect organisms! (what is perfect in one environment may not be perfect in another)