22344514 chapter 22 the mechanisms of evolution

8/8/2019 22344514 CHAPTER 22 the Mechanisms of Evolution

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2.1 What facts form the base of our understanding of evolution?

ee Web/ CD Tutorial 22.1

harles Darwin attributed changes in species over time to the possession of advantageouaits by some individuals. He understood that individuals do not evolve, but populations

volve when individuals with different heritable genotypes survive and reproduce at differtes.

daptation refers both to characteristics of organisms and the way those characteristicse acquired via natural selection.

he sum of all copies of all alleles at all loci found in the population constitutes its geneool and represents the genetic variation that results in different phenotypic traits upohich natural selection can act. Review Figure 22.3

rtificial selection and laboratory experiments demonstrate the existence of considerabenetic variation in most populations. Review Figure 22.5

lele frequencies measure the amount of genetic variation in a population; genotypeequencies show how a population's genetic variation is distributed among its memberseview Figure 22.6

ardy-Weinberg equilibrium predicts the allele frequencies in populations in the absenevolution. Deviation from these frequencies indicates the work of evolutionaryechanisms. Review Figure 22.7, Web/ CD Tutorial 22.2

2.2 What are the mechanisms of evolutionary change?

gration of individuals between populations results in gene flow .

small populations, genetic driftthe random loss of individuals and the alleles theyossessmay produce large changes in allele frequencies from one generation to the nexnd greatly reduce genetic variation. Review Figure 22.8

opulation bottlenecks occur when only a few individuals survive a random event,sulting in a drastic shift in allele frequencies within the population and the loss of

ariation. Similarly, a population established by a small number of individuals colonizing aew region may lose variation via a founder effect.

onrandom mating may result in genotype frequencies that deviate from HardyWeinbquilibrium.

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2.3 What evolutionary mechanisms result in adaptation?

ee Web/ CD Tutorial 22.3

tness is the reproductive contribution of a phenotype to subsequent generations relativthe contributions of other phenotypes.

hanges in numbers of offspring are responsible for changes in the absolute size of aopulation, but only changes in the relative success of different phenotypes within aopulation lead to changes in allele frequencies.

atural selection can act on traits with quantitative variation in several different ways,sulting in stabilizing, directional , or disruptive selection. Review Figure 22.12

exual selection is primarily about success in reproduction, not about success in survivaeview Figure 22.16 and 22.17

2.4 How is genetic variation maintained w ithin populations?

though genetic drift, stabilizing selection, and directional selection all tend to reduceenetic variation within populations, most populations have considerable genetic variation

eutral mutations, sexual recombination, and frequency-dependent selection can maintaienetic variation within populations.

eutral alleles do not affect the fitness of an organism, are not affected by naturalelection, and may accumulate or be lost by genetic drift.

exual reproduction generates countless genotypic combinations that increase thevolutionary potential of populations despite short-term disadvantages.

polymorphism may be maintained by frequency-dependent selection when the fitnea genotype depends on its frequency in a population.

enetic variation may be maintained by the existence of genetically distinct subpopulatiover geographic space. Review Figure 22.20

2.5 What are the constraints on evolution?

evelopmental processes constrain evolution because all evolutionary innovations areodifications of previously existing structures.

ost adaptations impose costs. An adaptation can evolve only if the benefits it confers

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xceed the costs it imposes, a situation that leads to trade-offs.

2.6 How have humans influenced evolution?

umans have become major agents of evolution as they attempt to control pests andseases, move species around the globe, and modify organisms via biotechnology. Humactivities are changing the climate and have greatly increased the rates of extinction of

her species.


22344514 chapter 22 the mechanisms of evolution

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