Chapter 16Chapter 16

Population Genetics and SpeciationPopulation Genetics and Speciation

ObjectivesObjectives

CLE 3210.5.3 CLE 3210.5.3 Explain how genetic Explain how genetic variation in a population and variation in a population and changing environmental conditions changing environmental conditions are associated with adaptation and are associated with adaptation and the emergence of new species.the emergence of new species.

Darwin’s Darwin’s FinchesFinches

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Five conditions under which Five conditions under which evolution may take placeevolution may take place

Genetic mutationsGenetic mutations Gene flowGene flow Genetic driftGenetic drift Nonrandom matingNonrandom mating Natural selection.Natural selection.

MutationMutation

MutationsMutations are changes in the DNA. are changes in the DNA.

Gene FlowGene Flow

EmigrationEmigration and and immigrationimmigration cause cause gene flowgene flow between populations and between populations and can thus affect gene frequencies.can thus affect gene frequencies.

Genetic DriftGenetic Drift

Genetic driftGenetic drift is a change in allele is a change in allele frequencies due to random events.frequencies due to random events.

Genetic drift operates most strongly Genetic drift operates most strongly in small populations.in small populations.

Nonrandom MatingNonrandom Mating

Mating is nonrandom whenever Mating is nonrandom whenever individuals may choose partnersindividuals may choose partners .. Sexual selectionSexual selection occurs when certain traits occurs when certain traits

increase an individual’s success at mating. increase an individual’s success at mating. Sexual selection explains the development Sexual selection explains the development

of traits that improve reproductive success of traits that improve reproductive success but that may harm the individual.but that may harm the individual.

Natural SelectionNatural Selection

Three general patternsThree general patterns Stabilizing SelectionStabilizing Selection

favors the formation of average traits. favors the formation of average traits. Disruptive SelectionDisruptive Selection

favors extreme traits rather than average traits.favors extreme traits rather than average traits. Directional SelectionDirectional Selection

favors the formation of more-extreme traits.favors the formation of more-extreme traits.

The Concept of SpeciesThe Concept of Species

Biological species conceptBiological species concept a species is a population of organisms a species is a population of organisms

that can successfully interbreed but that can successfully interbreed but cannot breed with other groupscannot breed with other groups

Isolation and SpeciationIsolation and Speciation

Geographic IsolationGeographic Isolation Results from the separation of population subgroups by Results from the separation of population subgroups by

geographic barriers.geographic barriers. Allopatric SpeciationAllopatric Speciation

Speciation due to separation of subgroups of a populationSpeciation due to separation of subgroups of a population Reproductive IsolationReproductive Isolation

Results from the separation of population subgroups by Results from the separation of population subgroups by barriers to successful breeding.barriers to successful breeding.

Sympatric SpeciationSympatric Speciation Reproductive isolation within the same geographic areaReproductive isolation within the same geographic area

Allopatry vs SympatryAllopatry vs Sympatry

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Reproductive isolation: Reproductive isolation: MonkeyflowerMonkeyflower

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Reproductive isolationReproductive isolation

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Rates of SpeciationRates of Speciation

GradualismGradualism species undergo small changes at a constant rate. species undergo small changes at a constant rate.

Punctuated equilibriumPunctuated equilibrium new species arise abruptly, differ greatly from their new species arise abruptly, differ greatly from their

ancestors, and then change little over long periods.ancestors, and then change little over long periods.

Variation of Traits Within a Variation of Traits Within a PopulationPopulation

Variations in genotype arise by Variations in genotype arise by mutation,mutation, recombinationrecombination, and the , and the random pairing of random pairing of gametes.gametes.

The Gene PoolThe Gene Pool

The total genetic information available in a The total genetic information available in a population is called the population is called the gene pool.gene pool.

Allele frequencyAllele frequency is determined by dividing is determined by dividing the total number of a certain allele by the total the total number of a certain allele by the total number of alleles of all types in the populationnumber of alleles of all types in the population

Predicting PhenotypePredicting Phenotype Phenotype frequency is equal to the number of Phenotype frequency is equal to the number of

individuals with a particular phenotype divided by individuals with a particular phenotype divided by the total number of individuals in the population.the total number of individuals in the population.

The Hardy-Weinberg Genetic The Hardy-Weinberg Genetic EquilibriumEquilibrium

Allele frequencies in the gene pool do not Allele frequencies in the gene pool do not change unless acted upon by certain forces.change unless acted upon by certain forces.

Hardy-Weinberg genetic equilibriumHardy-Weinberg genetic equilibrium is a is a theoretical model of a population in which no theoretical model of a population in which no evolution occurs and the gene pool of the evolution occurs and the gene pool of the population is stable.population is stable.

Phenotype FrequencyPhenotype Frequency

Calculating using the Hardy Calculating using the Hardy Weinberg equationWeinberg equation

Dominant allele frequency = pDominant allele frequency = p Recessive allele frequency = qRecessive allele frequency = q p + q = 1p + q = 1 pp22 +2pq+ q +2pq+ q22 = 1 = 1