Chapter 16 Evolution of Populations

1. Chapter 16Evolution of Populations Section 16-2 Evolution As Genetic Change

2. 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

3. Evolution Acts On Populations Does NOT Act On Individuals

4. 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

5. Camouflage

6. Camouflage

7. Camouflage

8. Natural Selection on Single Gene Traits BUT: What If Black Allowed The Lizard To Warm Up Faster & Move Quicker??????

9. Natural Selection on Polygenic Traits • Traits Controlled By More Than One Gene • Effects On Natural Selection Are More Complex

10. 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

11. 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

12. Directional Selection

13. 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

14. Stabilizing Selection

15. 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

16. Disruptive Selection

17. 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

18. 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

19. 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

20. 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

21. Founder Effect

22. 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

24. 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

25. 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

26. Random Mating All Members Of The Population Must have An Equal Opportunity To Produce Offspring

27. Large Population Genetic Drift Has Less Effect On Large Populations

28. No Movement Into or Out Of The Population New Alleles Must Not Enter Rare Alleles Must Not Be Allowed To Leave

29. No Mutations Mutations Introduce New Alleles Causing A Change In Allele Frequencies

30. No Natural Selection All Genotypes Must Have Equal Opportunity To Survive & Reproduce No Phenotype Can Have An Advantage Over Another