How can populations How can populations evolve to form new evolve to form new

species or to eliminate a species or to eliminate a species?species?

What causes a What causes a population’s gene pool to population’s gene pool to

change?change?

EvolutionEvolution

Karen A. RobinsonKaren A. Robinson

Evolution Topics Covered:Evolution Topics Covered:

Genes and evolutionGenes and evolution Changes in a population’s gene poolChanges in a population’s gene pool Formation of new speciesFormation of new species Genes tell evolutionary historyGenes tell evolutionary history

What is evolutionWhat is evolution

Evolution is defined as a change in the Evolution is defined as a change in the frequency of alleles in a population over time.frequency of alleles in a population over time.

I.I. Genes and EvolutionGenes and Evolution

Heredity is controlled by genesHeredity is controlled by genes Genes are carried on the chromosomesGenes are carried on the chromosomes Changes in genes or chromosomes create Changes in genes or chromosomes create

variationvariation Genetic variation is the cause for evolutionGenetic variation is the cause for evolution Evidence shows how evolution occursEvidence shows how evolution occurs Evidence shows why evolution occursEvidence shows why evolution occurs

II.II. Populations and Gene PoolsPopulations and Gene Pools

Genetic variation and evolution studiedGenetic variation and evolution studied Population: a group of species that interbreedPopulation: a group of species that interbreed Interbreeding produces a common gene poolInterbreeding produces a common gene pool Genes can have different alleles or versions of that Genes can have different alleles or versions of that

genegene Dominant and recessive allelesDominant and recessive alleles Allelic frequency is studiedAllelic frequency is studied

Evolution and Allelic FrequencyEvolution and Allelic Frequency

Evolution has occurred if change in allelic frequency Evolution has occurred if change in allelic frequency occurs.occurs.

Example- population contains:Example- population contains: 48% heterozygous black mice Bb48% heterozygous black mice Bb 36% homozygous brown mice bb36% homozygous brown mice bb 16% homozygous black mice BB16% homozygous black mice BB

B is the dominant allele (black) and is shown more B is the dominant allele (black) and is shown more frequently (36% + 16%= 52%)frequently (36% + 16%= 52%)

If the B allele drops to 30%, the population is evolving.If the B allele drops to 30%, the population is evolving.

How can we predict evolution How can we predict evolution will occur?will occur?

Hardy-Weinberg Principle states:Hardy-Weinberg Principle states: Allele frequencies in a population should remain Allele frequencies in a population should remain

constantconstant Factors cause those frequencies to changeFactors cause those frequencies to change Makes predictions for populationsMakes predictions for populations p squared + 2pq + q squared=1p squared + 2pq + q squared=1 Ex: p is dominant and q is recessiveEx: p is dominant and q is recessive www.pearsonsuccessnet.com will give more will give more

information regarding the Hardy-Weinberg information regarding the Hardy-Weinberg PrinciplePrinciple

III. Formation of a New SpeciesIII. Formation of a New Species

Speciation: formation of a new speciesSpeciation: formation of a new species Typically speciation is due to reproductive Typically speciation is due to reproductive

isolationisolation

Reproductive IsolationReproductive Isolation

Population will evolve into two separate Population will evolve into two separate speciesspecies

Due to:Due to: Behavioral Isolation Ex: differences in mating Behavioral Isolation Ex: differences in mating

ritualsrituals Geographic Isolation: two populations separated Geographic Isolation: two populations separated

by geographic barriersby geographic barriers Temporal Isolation: Two or more species Temporal Isolation: Two or more species

reproduce at different timesreproduce at different times

Evolution in a NutshellEvolution in a Nutshell

Evolution is a continuous processEvolution is a continuous process Evolutions is evident through fossil recordsEvolutions is evident through fossil records Evolution can be calculated using the Hardy-Evolution can be calculated using the Hardy-

Weinberg PrincipleWeinberg Principle Evolution is typically caused by environmental Evolution is typically caused by environmental

factorsfactors www.biologyjunction.com choose evolution choose evolution

for information regarding evolutionfor information regarding evolution

Questions????Questions????