how populations evolve. voyage of the beagle jean baptiste lamarck
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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
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