the evolution of populations

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The Evolution of Populations. Darwin and Mendels discoveries merged. Darwins theory of natural selection Mendels inheritable information Population Genetics: genetic variation within a population Modern Synthesis: 1940s; integrated discoveries Population is the unit of evolution - PowerPoint PPT Presentation


  • The Evolution of PopulationsDarwin and Mendels discoveries merged.Darwins theory of natural selectionMendels inheritable information

    Population Genetics: genetic variation within a population

    Modern Synthesis: 1940s; integrated discoveriesPopulation is the unit of evolutionNatural selection is means of mechanismGradualism: large changes evolve from small changes over long period of time.

  • Genotype FrequenciesPopulation:Localized group of individuals belonging to the same species.Species:Individuals that have the potential to interbreedand produce fertile offspring in nature.Gene Pool:Total aggregate of genes in a population at any on time. Consists of all alleles at all gene loci inall individuals of the populationDiploid, locus, fixed pop., Individuals are selected butPopulations evolve.

  • Imaginary Population of FlowersR is Dominant (Red), r is recessive (white)500 plants (20 are white, HR)480 are red meaning R? (HD or Ht)

    IF320 are RR and 160 are RrthenHow many copies of the gene are there in the population?How many genes are dominant? Recessive?What are the percentage of each1000 genes800 dominant200 recessive80%....20%

  • Hardy-Weinberg TheoremFrequencies of alleles and genotypes in a populations gene poolremains constant over the generations unless acted upon by other agents. The number of times an allele occurs within a population.p= frequency of dominant alleleq= frequency of recessive allelep+q=1

  • Hardy Weinberg Equationp2 + 2pq + q2 = 1Frequencyof AAgenotypeFrequencyof Aa +aAgenotypeFrequencyof aagenotypePKU: recessive allele disease1 in 10,000 births (q2=0.0001)

    What percentage of US population are carriers?

  • SolutionOne PKU per 10,000 births.q2 = 0.0001 frequencies of HRTherefore.q = 0.0001 = 0.01 Frequency of Reccesive AlleleFrequency of Allele is p + q = 1 and if q = 0.01then p = 0.99Now using HW Equation solve for 2pq2pq = 2 x 0.99 x 0.01 = 0.0198 or close to 2%2% of the Population are PKU Carriers.

  • You SolveAllele Frequency of B is 0.7, what would the frequency of heterozygotes by if in HW equilibrium? Frequency of recessive allele?

    313 out of 1432 individuals have a recessive disorder. What percentage of this population are carriers?If 511 individual out of 2315 show the characteristic of a DOMINANT disorder, what is the frequency of the recessive allele? How many individuals would be show the recessive trait?0.42 0.3050%0.53 648 INDIV.

  • MicroevolutionChanges of the gene pool of a population at the smallest level.Frequencies of Allele in a population. 5 Conditions needed for HW Eq.Very Large Populations: Isolation from other populationsNo Net MutationsRandom MatingNo Natural SelectionA deviation from HW eq. in a gene pool signifies evolutionNatural Population are not EXPECTED to be in HW eq.

  • 5 Agents of Microevolution1. Genetic Drift: changes in the gene pool of a small population

  • Genetic Drift can be caused by:A. Bottleneck effect: Disaster eliminates large population. Surviving population is not represented of the original. Genetic variability is lowThe Founder Effect: Genetic drift may occur when a smaller colony breaks away from original. (Darwins Finches)

  • Cause of Microevolution Cont.Gene Flow: genetic exchange due to alleles migrating in or out of a population. Will tend to reduce differences b/w populations.Mutations: Change in DNA of an organism. Mustoccur in gametes, rare occurrence of this occurring.

  • Cause of Microevolution Cont.Nonrandom Mating: Inbreeding; relative frequency of genotypes deviate from H-W.W/ each generation Heterozygote # decreases.Assortive Mating: selecting partners with similar characteristics.Natural Selection: differential success of reproduction. Most likely agent to causemicroevolution. Selects favorable genotypes

  • Inheritable VariationsDifferences can occur between populationsQuantitative Variations occur along a continuum.Polymorphism: Two or more contrasting forms (morphs) of a characteristic. High frequency of alleles of all forms.Ex: garter snakes, freckles, Blood type (ABO).

  • Variation Between PopulationsGeographical Variations: differences b/w pop (or w/i). due to environmental factors. Natural selection andgenetic drift can cause. Cline: graded change in a trait along a geographicaxis.

  • Mutations generate Genetic VariationsMutation: Point mutations mostly harmless, occurin somatic cells. Rarely will cause mutantallele allowing for better reproduction success.Chromosomal Mutation: disrupts developmentmay have benefits.Bacteria: reproduce every 20 minutes, mutationin one may produce millions in an hour.Antibiotic resistant bacteria

  • Natural Selection as a means of EvolutionDarwinian Fitness: the measure that is critical to selection, is the relative contribution anindividual makes to the gene pool of the next generation.Relative Fitness: contribution of a genotype to thenext generation compared to another. Based asa % based on best reproductive member (1).

  • Diversifying Selection: environmental factorsfavors extreme individuals at both ends.Directional Selection: changes that occur whenmoving to new area with different conditions.Stabilizing Selection: cuts extreme varients, reduce phenotypic variation, status quoModes of Selections

  • Natural Selection and PerfectionNatural Selection cannot produce perfectionWHY???Evolution is limited by historical constraintsAdaptations are often compromisedNot all evolution is adaptiveSelection can only edit existing variations