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Chapter 16 Evolution of Populations. Section 16-2 Evolution As Genetic Change. Natural Selection. Does NOT Act Directly On Genes Does Act On Phenotypes The Phenotype Gives The Survival Edge Survivors Must Reproduce Alters Relative Frequency of Alleles Over Time. Evolution.

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Chapter 16 evolution of populations

Chapter 16Evolution of Populations

Section 16-2

Evolution As Genetic Change


Natural selection
Natural Selection

Does NOT Act Directly On Genes

  • Does Act On Phenotypes

    • The Phenotype Gives The Survival Edge

    • Survivors Must Reproduce

      • Alters Relative Frequency of Alleles Over Time


Evolution
Evolution

Acts On Populations

Does NOT Act On Individuals


Natural selection on single gene traits
Natural Selection on Single Gene Traits

Key Concept

Natural Selection On Single-Gene Traits Can Lead To Changes In Allele Frequencies And Thus To Evolution





Natural selection on single gene traits1
Natural Selection on Single Gene Traits

BUT:

What If Black Allowed The Lizard To Warm Up Faster & Move Quicker??????


Natural selection on polygenic traits
Natural Selection on Polygenic Traits

  • Traits Controlled By More Than One Gene

    • Effects On Natural Selection Are More Complex


Natural selection on polygenic traits1
Natural Selection on Polygenic Traits

Key Concept

Natural Selection Can Affect The Distribution Of Phenotypes In Any Of Three Ways:

  • Directional Selection

  • Stabilizing Selection

  • Disruptive Selection


Directional selection
Directional Selection

  • Individuals At One End Of The Standard Curve Have Higher Fitness Than Individuals In The Middle, Or At The Other End

    • Curve Moves, Over Time, Toward The End With Increased Fitness



Stabilizing selection
Stabilizing Selection

When Individuals Near

The Center Of The Standard Curve Have Higher Fitness

Than Individuals On Either End

May Narrow The Curve

Example: Human Birth Weight



Disruptive selection
Disruptive Selection

When Individuals At The

Upper And The Lower End

Have Higher Fitness Than Individuals Near The Middle.

If Severe Enough, May Cause The Development Of TWO Phenotypes



Genetic drift
Genetic Drift

  • Natural Selection Is Not The Only Source of Evolutionary Change

  • In Small 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 Drift Is

    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

        • Hawaiian Fruit Flies

        • Darwin’s Finches

        • Hawaiian Honey Creepers



Genetic drift4
Genetic Drift

  • Circumstances That May Result In Genetic Drift: (cont.)

    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


Evolution vs genetic equilibrium
Evolution vs. Genetic Equilibrium

Under What Conditions Will Evolution NOT Occur:

  • Random Mating

  • Population Must Be Very Large

  • No Movement In or Out of Pop.

  • No Mutations

  • No Natural Selection


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 Population Must have An Equal Opportunity To Produce Offspring


Large population
Large Population

Genetic Drift Has Less Effect On 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 Not Be Allowed To Leave


No mutations
No Mutations

Mutations Introduce New Alleles Causing A Change In Allele Frequencies


No natural selection
No Natural Selection

All Genotypes Must Have Equal Opportunity To Survive & Reproduce

No Phenotype Can Have An Advantage Over Another


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