Ch. 16 Evolution Ch. 16 Evolution of Populationsof Populations

Variations and Gene PoolsVariations and Gene Pools

Gene poolGene pool – consists of all genes, – consists of all genes, including all the different alleles, that are including all the different alleles, that are present in a population.present in a population.

Relative frequencyRelative frequency – the number of times – the number of times that the allele occurs in a gene pool, that the allele occurs in a gene pool, compared with the number of times other compared with the number of times other alleles for the same gene occur.alleles for the same gene occur.

Variations and Gene PoolsVariations and Gene Pools

Sources of Genetic VariationSources of Genetic Variation

The 2 main sources of genetic variation The 2 main sources of genetic variation are are mutations mutations & the & the genetic shufflinggenetic shuffling that results from sexual reproduction.that results from sexual reproduction.

Single-Gene & Polygenic Single-Gene & Polygenic TraitsTraits

The # of phenotypes produced for a given The # of phenotypes produced for a given trait depend on how many genes control trait depend on how many genes control the trait.the trait.

Single-gene traitSingle-gene trait - controlled by a single - controlled by a single gene, that gene, that

has 2 alleleshas 2 alleles Ex.) Widow’s PeakEx.) Widow’s Peak

Single-Gene & Polygenic Single-Gene & Polygenic TraitsTraits

Polygenic traitsPolygenic traits - trait controlled by 2 or - trait controlled by 2 or more genesmore genes Ex.) Height in humansEx.) Height in humans

Evolution as Genetic ChangeEvolution as Genetic Change

Evolutionary fitnessEvolutionary fitness can be viewed as an can be viewed as an organism’s success in passing genes to the next organism’s success in passing genes to the next generation.generation.

Evolutionary adaptationEvolutionary adaptation can be viewed as any can be viewed as any genetically controlled trait that increases an genetically controlled trait that increases an individual’s ability to pass along its genes.individual’s ability to pass along its genes.

Evolution as Genetic ChangeEvolution as Genetic Change

NS never acts directly on genes.NS never acts directly on genes. NS can only affect which individuals NS can only affect which individuals

survive & reproduce, & which do not.survive & reproduce, & which do not. Also, remember that it is populations, not Also, remember that it is populations, not

individual organisms, that can evolve over individual organisms, that can evolve over time.time.

NS on Single-Gene TraitsNS on Single-Gene Traits

NS on single-gene traits can lead to NS on single-gene traits can lead to changes in allele frequencies & thus to changes in allele frequencies & thus to evolution.evolution.

NS on Polygenic TraitsNS on Polygenic Traits

NS can affect the distributions of NS can affect the distributions of phenotypes in any of 3 ways: phenotypes in any of 3 ways:

--directional selectiondirectional selection

--stabilizing selectionstabilizing selection

--disruptive selectiondisruptive selection

NS on Polygenic TraitsNS on Polygenic Traits

Directional SelectionDirectional Selection - occurs when - occurs when individuals at 1 end of the curve have individuals at 1 end of the curve have higher fitness than individuals in the higher fitness than individuals in the middle or at the other end.middle or at the other end.

NS on Polygenic TraitsNS on Polygenic Traits

Stabilizing selectionStabilizing selection - occurs when - occurs when individuals near individuals near

the center of a curvethe center of a curve

have higher fitness have higher fitness

than individuals at than individuals at

either end.either end.

NS on Polygenic TraitsNS on Polygenic Traits

Disruptive selectionDisruptive selection - when individuals at - when individuals at the upper & lower ends of the curve have the upper & lower ends of the curve have higher fitness than individuals near the higher fitness than individuals near the middle.middle.

Genetic DriftGenetic Drift

Genetic driftGenetic drift – random change in allele – random change in allele frequencies that occurs in small frequencies that occurs in small populations.populations.

Founder effectFounder effect - situation in which allele - situation in which allele frequencies change as a result of the frequencies change as a result of the migration of a small subgroup of a migration of a small subgroup of a population.population.

Genetic DriftGenetic Drift

Evolution vs. Genetic Evolution vs. Genetic EquilibriumEquilibrium

Hardy-Weinberg PrincipleHardy-Weinberg Principle-allele -allele frequencies in a population will remain frequencies in a population will remain constant unless one or more factors cause constant unless one or more factors cause those frequencies to change.those frequencies to change.

Genetic equilibriumGenetic equilibrium - when allele - when allele frequencies remain constant, the frequencies remain constant, the population will not evolve.population will not evolve.

Evolution vs. Genetic Evolution vs. Genetic EquilibriumEquilibrium

5 conditions are required to maintain genetic 5 conditions are required to maintain genetic equilibrium:equilibrium:

-random mating-random mating

-large population-large population

-no movement into/out of pop.-no movement into/out of pop.

-no mutations-no mutations

-no NS-no NS

Overuse of AntibioticsOveruse of Antibiotics

People may be overusing antibiotics.People may be overusing antibiotics. Doctors may prescribe them for diseases Doctors may prescribe them for diseases

which they are not effective.which they are not effective. This wide use of antibiotics has caused This wide use of antibiotics has caused

many bacteria to evolve resistance to many bacteria to evolve resistance to antibiotics.antibiotics.

The Process of SpeciationThe Process of Speciation

SpeciationSpeciation - formation of a new species - formation of a new species The gene pools of 2 populations must The gene pools of 2 populations must

become separated for them to become become separated for them to become new species.new species.

Isolating MechanismsIsolating Mechanisms

As new species evolve, populations As new species evolve, populations become reproductively isolated from each become reproductively isolated from each other.other.

Reproductive isolationReproductive isolation - when members - when members of 2 populations can’t interbreed & of 2 populations can’t interbreed & produce fertile offspringproduce fertile offspring

Isolating MechanismsIsolating Mechanisms

Behavioral isolationBehavioral isolation - when 2 - when 2 populations are capable of interbreeding populations are capable of interbreeding but have differences in courtship rituals or but have differences in courtship rituals or other reproductive strategies that involve other reproductive strategies that involve behaviorbehavior Ex.) Birds with Ex.) Birds with different different

mating songsmating songs

Isolating MechanismsIsolating Mechanisms

Geographic isolationGeographic isolation - 2 populations are - 2 populations are separated by geographic barriers like separated by geographic barriers like rivers, mountains, or bodies of waterrivers, mountains, or bodies of water Ex.) Squirrels split by Colorado RiverEx.) Squirrels split by Colorado River

Isolating MechanismsIsolating Mechanisms

Temporal isolationTemporal isolation - when 2 or more - when 2 or more species reproduce at different timesspecies reproduce at different times Ex.) Orchids releasing pollen on Ex.) Orchids releasing pollen on

different daysdifferent days

Testing NS Testing NS in in

NatureNature

Speciation in Speciation in Darwin’s FinchesDarwin’s Finches

Speciation in the Galapagos Speciation in the Galapagos finches occurred by: finches occurred by:

founding a new populationfounding a new population geographic isolationgeographic isolation changes in the new population’s genechanges in the new population’s gene poolpool reproductive isolation reproductive isolation ecological competitionecological competition

Patterns of EvolutionPatterns of Evolution

MacroevolutionMacroevolution - large-scale evolutionary - large-scale evolutionary patterns & processes that occur over long patterns & processes that occur over long periods of timeperiods of time

6 important topics in macroevolution are: 6 important topics in macroevolution are: • extinctionextinction• adaptive radiationadaptive radiation• convergent evolutionconvergent evolution• coevolution, coevolution, • punctuated equilibrium, punctuated equilibrium, • changes in developmental geneschanges in developmental genes

Patterns of EvolutionPatterns of Evolution

Extinction:Extinction: More than 99% of all species are now extinctMore than 99% of all species are now extinct It usually happens for a reason; species It usually happens for a reason; species

compete for resources, & environments compete for resources, & environments changechange

Some species adapt & Some species adapt & survive, others become survive, others become

extinctextinct

Patterns of EvolutionPatterns of Evolution

Adaptive radiationAdaptive radiation - when a single species - when a single species has evolved, through NS, into diverse has evolved, through NS, into diverse forms that live in different waysforms that live in different ways Ex.) Darwin’s FinchesEx.) Darwin’s Finches

Patterns of EvolutionPatterns of Evolution

Convergent evolutionConvergent evolution - when unrelated - when unrelated organisms begin to resemble one anotherorganisms begin to resemble one another It has occurred in both plants It has occurred in both plants

& animals & animals Ex.) Swimming animalsEx.) Swimming animals

Patterns of EvolutionPatterns of Evolution

CoevolutionCoevolution - when 2 species evolve in - when 2 species evolve in response to changes in each other over response to changes in each other over timetime Ex.) Orchid has long spur with nectar in its tip, Ex.) Orchid has long spur with nectar in its tip,

a Hawk moth has equally long feeding tube a Hawk moth has equally long feeding tube that allows it to feed on the nectar that allows it to feed on the nectar

Patterns of EvolutionPatterns of Evolution

Punctuated equilibriumPunctuated equilibrium - a pattern of long, - a pattern of long, stable periods interrupted by brief periods stable periods interrupted by brief periods of more rapid changeof more rapid change