SpeciationSpeciation

Gene poolGene pool

The total of all the genes in aThe total of all the genes in apopulation is called the population is called the gene gene pool.pool. The frequency of an allele The frequency of an alleleof a gene in that population,of a gene in that population,relative to others is the relative to others is the genegenefrequency.frequency.

As long as a population is largeAs long as a population is largeand mating is random, geneand mating is random, genefrequencies remain constant i.e.frequencies remain constant i.e.in in genetic equilibrium. genetic equilibrium.

Alteration to gene poolAlteration to gene pool

Can occur in a number of ways:Can occur in a number of ways:

MutationMutation Natural selectionNatural selection Gene migration (immigrants Gene migration (immigrants

arriving from another arriving from another population)population)

Non-random mating Non-random mating (inbreeding)(inbreeding)

Genetic drift (isolation of a Genetic drift (isolation of a group)group)

Chance (e.g. a rare allele lost Chance (e.g. a rare allele lost in a forest fire)in a forest fire)

SpeciesSpeciesA species is a group ofA species is a group oforganisms that share commonorganisms that share commonphysiological characteristics andphysiological characteristics andhave the same chromosomehave the same chromosomecomplement.complement.

Members of a species canMembers of a species caninterbreed and produce interbreed and produce fertile fertile offspring.offspring.

Species are Species are reproductivelyreproductivelyisolatedisolated from other groups (i.e. from other groups (i.e. other species)other species)

SpeciationSpeciation

Speciation is the formation ofSpeciation is the formation ofnew species and is driven bynew species and is driven byevolution. It involves changes toevolution. It involves changes tothe phenotype and genotype of athe phenotype and genotype of apopulation.population.

When a population of a speciesWhen a population of a speciesbecomes split, becomes split, sub-populationssub-populationsare formed. A barrier may existare formed. A barrier may existbetween sub-populationsbetween sub-populationspreventing gene exchangepreventing gene exchange

Isolating barriers may be:Isolating barriers may be:

Geographical (e.g. rivers, Geographical (e.g. rivers, seas, mountains)seas, mountains)

Ecological (e.g. temperature, Ecological (e.g. temperature, food, humidity)food, humidity)

Reproductive (e.g. different Reproductive (e.g. different populations being sexually populations being sexually receptive in different seasons)receptive in different seasons)

Top Tip and Handy Hint:Top Tip and Handy Hint:

G G eographicaleographicalE E cologicalcologicalRR eproductive eproductiveMM echanisms echanisms

http://www.okc.cc.ok.us/biologylabs/Documents/Evolution/Speciation.htm

http://www.mhhe.com/biosci/esp/2001_gbio/folder_structure/ev/m3/s2/evm3s2_4.htm

Population APopulation A Population BPopulation B

Originally population A & B Originally population A & B identical and interbreed (gene identical and interbreed (gene flow occurs)flow occurs)

A&B become isolated (GERM)A&B become isolated (GERM) Mutation occurs in population B Mutation occurs in population B

that makes it less visible to that makes it less visible to predatorspredators

Mutated form naturally selected Mutated form naturally selected for and becomes the norm in for and becomes the norm in population Bpopulation B

Population APopulation A Population Population BB

Isolating mechanism removedIsolating mechanism removed Populations can no longer Populations can no longer

exchange genes as they are exchange genes as they are now so different and now so different and reproductively isolated from reproductively isolated from each othereach other

Continental distribution of Continental distribution of organismsorganisms

Different regions of the world can Different regions of the world can be divided up in terms of the be divided up in terms of the faunafauna they possessthey possess

Mammals in Europe, for example, Mammals in Europe, for example, differ greatly from the marsupials of differ greatly from the marsupials of AustraliaAustralia

Such continental distribution is Such continental distribution is thought to have arisen from thought to have arisen from continental driftcontinental drift, i.e. where land , i.e. where land masses were previously joined masses were previously joined together millions of years ago, they together millions of years ago, they gradually drifted apart.gradually drifted apart.

Populations therefore became Populations therefore became separated by such barriers as separated by such barriers as oceans, mountains and desertsoceans, mountains and deserts