Evolution as Genetic Evolution as Genetic Change and SpeciationChange and Speciation

A Population’s Gene PoolA Population’s Gene Pool

A A gene poolgene pool is all is all the alleles available the alleles available in all of the in all of the individuals in a individuals in a populationpopulation

How do we know a population How do we know a population is evolving?is evolving?

When there are changes in the frequency of When there are changes in the frequency of alleles in the gene pool (aka alleles in the gene pool (aka MicroevolutionMicroevolution))

How do the allele frequencies change?How do the allele frequencies change? Natural Selection (directional, stabilizing, Natural Selection (directional, stabilizing,

disruptive, or sexual selection)disruptive, or sexual selection) Random Change (mutations, genetic drift, or Random Change (mutations, genetic drift, or

gene flow)gene flow) MigrationMigration

Genetic DriftGenetic Drift The random change in the The random change in the

gene pool of a populationgene pool of a population All populations are subject to All populations are subject to

genetic drift, but genetic drift, but smallsmall populations are impacted morepopulations are impacted more

Bottleneck Effect:Bottleneck Effect: Occurs when Occurs when a natural disaster greatly a natural disaster greatly reduces the size of the reduces the size of the population and the gene pool population and the gene pool (population loses variation)(population loses variation)

Founder Effect:Founder Effect: Occurs when a Occurs when a few individuals from a few individuals from a population colonize an isolated population colonize an isolated island or new habitat island or new habitat (population loses genetic (population loses genetic variation)variation)

Gene FlowGene Flow

Gene flow occurs when genes are Gene flow occurs when genes are exchanged with another population exchanged with another population (ex: migration)(ex: migration)

Gene flow can reduce genetic Gene flow can reduce genetic differences between populations, differences between populations, possibly uniting the gene pool in a possibly uniting the gene pool in a single populationsingle population

MutationsMutations

The random change in the DNA of an The random change in the DNA of an organismorganism

The frequency of a mutation in the The frequency of a mutation in the population will depend on the effects population will depend on the effects of natural selection- of natural selection- will it make the will it make the individual more likely to survive and individual more likely to survive and reproduce?reproduce?

Hardy-Weinberg EquilibriumHardy-Weinberg Equilibrium

Evolution will NOT occur (allele Evolution will NOT occur (allele frequencies remain constant) if the frequencies remain constant) if the following conditions are met:following conditions are met:

1.1. Random matingRandom mating

2.2. No emigration or immigrationNo emigration or immigration

3.3. Population must be largePopulation must be large

4.4. No natural selectionNo natural selection

5.5. No mutationsNo mutations

Evolution of a SpeciesEvolution of a Species Biological Species Concept:Biological Species Concept: a species a species

is a population that will interbreed is a population that will interbreed and produce fertile offspringand produce fertile offspring

When a population evolves enough When a population evolves enough genetic change (either through genetic change (either through natural selection, genetic drift, etc.) natural selection, genetic drift, etc.) that it no longer interbreeds with the that it no longer interbreeds with the original population, it is considered a original population, it is considered a new speciesnew species

An Example of SpeciationAn Example of Speciation1.1. A species contains one A species contains one

population or several population or several interbreeding populationsinterbreeding populations

2.2. A barrier comes between A barrier comes between the populationsthe populations

3.3. Natural selection occursNatural selection occurs

4.4. Barrier is removed, Barrier is removed, reproductive isolation has reproductive isolation has occurred, two species now occurred, two species now existexist

Other Reproductive BarriersOther Reproductive Barriers

Temporal (timing)- different mating Temporal (timing)- different mating seasonsseasons

Behavioral- different courtship or mating Behavioral- different courtship or mating behaviorsbehaviors

Habitat- Fish living in streams verses open Habitat- Fish living in streams verses open waterwater

Geographic- populations divided by Geographic- populations divided by barriers like glaciers, valleys, rivers, etc.barriers like glaciers, valleys, rivers, etc.