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Evolution of Populations. Other Mechanisms of Genetic Change. Gene Flow. Movement of Alleles From One Population To Another Increases Genetic Variation Of The Receiving Population Less Gene Flow – More Differences Between Populations

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evolution of populations

Evolution of Populations

Other Mechanisms of Genetic Change

gene flow
Gene Flow

Movement of Alleles

From One Population

To Another

  • Increases Genetic Variation Of The Receiving Population
  • Less Gene Flow – More Differences Between Populations
    • Increases Probability of Each Population Becoming Separate Species.
genetic drift
Genetic Drift
  • Natural Selection Is Not The Only Source of Evolutionary Change
  • InSmall Populations
    • An Allele Can Become More Or Less Common By Chance
genetic drift1
Genetic Drift
  • Smaller Populations
    • Can Have Shifts In The Relative Frequency Of Alleles Much Faster Than Larger Populations
    • Their Gene Pool Is Smaller

Genetic DriftIs

The Random Change

In Allele Frequency

genetic drift2
Genetic Drift

Key Concept:

In Small Populations,

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

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

genetic drift3
Genetic Drift
  • Circumstances That May Result In Genetic Drift:
    • Founder Effect
      • Colonization Of A New Habitat By A Small Number of Individuals
        • Hawaiian Fruit Flies
        • Darwin’s Finches
        • Hawaiian Honey Creepers
genetic drift4
Genetic Drift

The Bottleneck Effect

  • Occurs When Man Made, or Natural Disasters Destroy Most Of A Population.
  • The Remaining Members Usually Possess A Severely Diminished Gene Pool
hardy weinberg principle 1908
Hardy-Weinberg Principle (1908)

Key Concept:

Five Conditions Are Required To Maintain Genetic Equilibrium From Generation To Generation:

  • There Must Be Random Mating
  • The Population Must Be Very Large
  • There Can Be No Movement In or Out Of The Population
  • No Mutations
  • No Natural Selection
random mating
Random Mating

All Members Of The PopulationMust have An Equal OpportunityTo Produce Offspring

large population
Large Population

Genetic DriftHas Less EffectOn Large Populations

no movement into or out of the population
No Movement Into or Out Of The Population
  • New Alleles Must Not Enter
  • Rare Alleles Must NotBe Allowed To Leave
no mutations
No Mutations

Mutations Introduce New Alleles Causing A Change InAllele Frequencies

no natural selection
No Natural Selection

All GenotypesMust Have Equal OpportunityTo Survive & Reproduce

No PhenotypeCan Have An AdvantageOver Another

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