Evolution

EvolutionHow Populations Evolve

Voyage of the Beagle

Jean Baptiste LamarckCharles Lyell

Artificial Selection

Artificial Selection

Natural SelectionDarwin saw natural selection as the basic mechanism of evolutionAs a result, the proportion of individuals with favorable characteristics increasesAllele frequencies (and therefore phenotypes within a population) gradually change over time

These five canine species evolved from a common ancestor through natural selectionFigure 13.4C

African wilddogCoyoteFoxWolfJackalThousands tomillions of yearsof natural selectionAncestral canineThe evolution of insecticide resistance is an example of natural selection in actionFigure 13.5B

Chromosome with geneconferring resistanceto insecticideAdditionalapplications of thesame insecticide willbe less effective, andthe frequency ofresistant insects inthe populationwill growSurvivorInsecticideapplicationFossils provide strong support for evolution

Ammonite casts; Fossilized leaf

Other evidence for evolution comes fromComparative anatomy (e.g. homologous structures)

Biogeography

Comparative Embryology

Comparative Embryology

Molecular biology

Examples of natural selection camouflage adaptations in different environments

Population Genetics and Modern Evolutionary Synthesis TheoryPopulation geneticsStudies how populations change genetically over timeThe modern evolutionary synthesis theoryConnects Mendelian Inheritance, Darwins theory with population geneticsGene pool Is the total collection of genes in a population at any one timeMicroevolutionIs a change in the relative frequencies of alleles in a given gene pool

Gene pool in a nonevolving population remains constant over generations.

Hardy-Weinberg PrincipleStates that allele and genotype frequency in a population remain constant (equilibrium) from generation to generation unless an outside influence disturbs the balance.

Hardy-Weinberg PrincipleMust satisfy five conditionsThe population is very largeThe population is isolatedMutations do not alter the gene poolMating is randomAll individuals are equal in reproductive success

Hardy-Weinberg Equationp2 + 2pq + q2 = 1

p + q = 1

Wherep is frequency of the dominant allele; q is the frequency of the recessive allelep2 is the frequency of the homozygous dominant genotype2pq is the frequency of the heterozygous genotypeq2 is the frequency of the homozygous recessive genotypeThe Hardy-Weinberg equation is useful in public health sciencePublic health scientists use the Hardy-Weinberg equation To estimate frequencies of disease-causing alleles in the human population

Other contributors to evolution includeGenetic Drift change in the relative frequency of an alleleBottleneck effectFounder effect

Gene Flow movement of alleles from one population to anotherEmigration/immigration

Bottleneck Effect

Founder Effect

Loss of genetic variability when a new population is established by a very small number of individuals from a larger population.Founder Effect

PolydactylismIsland of Krakotoa, 1883Variation is extensive in most populationsMany populations exhibit polymorphism Different forms of phenotypic characteristicsFunctions to retain variety of morphs in a population living in a varied environment

0VARIATION AND NATURAL SELECTION

Polymorphism

Populations may also exhibit geographic variationVariation of an inherited characteristic along a geographic continuum0

Sexual recombination

Evolutionary Fitness?

Natural selection can alter variation in a population in three waysStabilizing selection

Directional selection

Disruptive selectionModes of Selection

Sexual selection may produce sexual dimorphismSexual selection leads to the evolution of secondary sexual characteristicsWhich may give individuals an advantage in mating0

Figure 13.17A

Figure 13.17B

Processes and Mechanisms of EvolutionAdaptation Genetic driftGene flowMutationsNatural selectionSpeciation