Download - Evolution of Populations

Foothill High School Science DepartmentFoothill High School Science Department

Evolution of PopulationsEvolution of Populations

Other Mechanisms of Genetic ChangeOther Mechanisms of Genetic Change


Gene FlowGene Flow

Movement of Movement of AllelesAlleles

From One PopulationFrom One Population

To AnotherTo Another• Increases Genetic Variation Of The Receiving Increases Genetic Variation Of The Receiving

PopulationPopulation• Less Gene Flow – More Differences Between Less Gene Flow – More Differences Between

PopulationsPopulations– Increases Probability of Each Population Increases Probability of Each Population

Becoming Separate Species.Becoming Separate Species.


Genetic DriftGenetic Drift

• Natural Selection Is Not The Only Natural Selection Is Not The Only Source of Evolutionary ChangeSource of Evolutionary Change

• InIn Small PopulationsSmall Populations– An Allele Can Become More Or Less An Allele Can Become More Or Less

Common Common By ChanceBy Chance



• Smaller Populations Smaller Populations – Can Have Shifts In The Relative Frequency Can Have Shifts In The Relative Frequency

Of Alleles Much Faster Than Larger Of Alleles Much Faster Than Larger PopulationsPopulations

– Their Gene Pool Is SmallerTheir Gene Pool Is Smaller

Genetic DriftGenetic Drift IsIs

The Random ChangeThe Random Change

In Allele FrequencyIn Allele Frequency



Key ConceptKey Concept:In Small Populations, In Small Populations,

Individuals That Carry A Particular Allele Individuals That Carry A Particular Allele May Leave More Descendents Than Other May Leave More Descendents Than Other Individuals, Just By Chance. Individuals, Just By Chance.

Over Time, A Series Of Chance Occurrences Over Time, A Series Of Chance Occurrences Of This Type Can Cause An Allele To Of This Type Can Cause An Allele To Become Common In A PopulationBecome Common In A Population



• Circumstances That May Result In Circumstances That May Result In Genetic Drift:Genetic Drift:

–Founder EffectFounder Effect• Colonization Of A New Habitat By A Colonization Of A New Habitat By A

Small Number of IndividualsSmall Number of Individuals–Hawaiian Fruit FliesHawaiian Fruit Flies–Darwin’s FinchesDarwin’s Finches–Hawaiian Honey CreepersHawaiian Honey Creepers


Founder EffectFounder Effect



The Bottleneck EffectThe Bottleneck Effect• Occurs When Man Made, or Natural Occurs When Man Made, or Natural

Disasters Destroy Most Of A Disasters Destroy Most Of A Population.Population.

• The Remaining Members Usually The Remaining Members Usually Possess A Severely Diminished Possess A Severely Diminished Gene PoolGene Pool


Hardy-Weinberg Principle (1908)Hardy-Weinberg Principle (1908)

Key ConceptKey Concept:Five Conditions Are Required To Maintain Five Conditions Are Required To Maintain

Genetic Equilibrium From Generation To Genetic Equilibrium From Generation To Generation:Generation:

1.1. There Must Be Random MatingThere Must Be Random Mating2.2. The Population Must Be Very LargeThe Population Must Be Very Large3.3. There Can Be No Movement In or Out Of There Can Be No Movement In or Out Of

The PopulationThe Population4.4. No MutationsNo Mutations5.5. No Natural SelectionNo Natural Selection


Random MatingRandom Mating

All Members Of The All Members Of The PopulationPopulation

Must have An Equal Must have An Equal OpportunityOpportunity

To Produce OffspringTo Produce Offspring


Large PopulationLarge Population

Genetic DriftGenetic DriftHas Less EffectHas Less Effect

On Large PopulationsOn Large Populations


No Movement Into or Out Of The PopulationNo Movement Into or Out Of The Population

• New Alleles Must Not EnterNew Alleles Must Not Enter

• Rare Alleles Must NotRare Alleles Must NotBe Allowed To LeaveBe Allowed To Leave


No MutationsNo Mutations

Mutations Introduce New Mutations Introduce New Alleles Causing A Change InAlleles Causing A Change In

Allele FrequenciesAllele Frequencies


No Natural SelectionNo Natural Selection

All GenotypesAll GenotypesMust Have Equal OpportunityMust Have Equal Opportunity

To Survive & ReproduceTo Survive & Reproduce

No PhenotypeNo PhenotypeCan Have An AdvantageCan Have An Advantage

Over AnotherOver Another

Download - Evolution of Populations

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