1. Natural Selection Understanding The Mechanism for Evolution

2. Natural Selection and Evolution Genetic Variability arises fromGenetic Variability arises from –mutation –sexual reproduction Natural Selection acts on individuals, favoring those with adaptations to the current environmentNatural Selection acts on individuals, favoring those with adaptations to the current environment Evolution occurs in populations as the individuals with greatest fitness leave the most offspringEvolution occurs in populations as the individuals with greatest fitness leave the most offspring

3. Hardy-Weinberg Equilibrium A condition where allele frequencies andA condition where allele frequencies and genotypic frequencies remain constant from generation to generation genotypic frequencies remain constant from generation to generation Changes from equilibrium values are used to determine if natural selection is occurringChanges from equilibrium values are used to determine if natural selection is occurring

4. Calculating Allele Frequencies In a population of 100 pea plants, there are 200 alleles for seed color. If 60 of those alleles are y for green color, what is the frequency of the y allele?In a population of 100 pea plants, there are 200 alleles for seed color. If 60 of those alleles are y for green color, what is the frequency of the y allele? Total number of alleles = 200Total number of alleles = 200 Total number of y alleles = 60Total number of y alleles = 60 y/total= 60/200 = 0.30y/total= 60/200 = 0.30

5. Conditions of Hardy-Weinberg Equilibrium Large population size Large population size Random mating Random mating No migration No migration No mutation No mutation No selection No selection

6. Conditions of Hardy-Weinberg Equilibrium Condition Non-equilibrium Condition Large Population Size Genetic Drift: Changes in allele frequency due to small population sizes 1. Founder effect 1. Founder effect 2. Population Bottleneck 2. Population Bottleneck

7. Conditions of Hardy-Weinberg Equilibrium Condition Non-equilibrium Condition Random Mating Non-random mating: Alters genotypic frequencies

8. Conditions of Hardy-Weinberg Equilibrium Condition Non-equilibrium Condition No Migration Migration: Can add new alleles, remove alleles or change allele frequency

9. Migration Contributes to Gene Flow Gene FlowGene Flow –Spreads advantageous alleles throughout the species –Helps maintain all the organisms over a large area as one species

10. Conditions of Hardy-Weinberg Equilibrium Condition Non-equilibrium Condition No Mutation Mutation: Alters allele frequency, causes formation of new genotypes

11. Conditions of Hardy-Weinberg Equilibrium Condition Non-equilibrium Condition No Selection Natural Selection: Increases frequency of genotypes with higher fitness

12. Types of Natural Selection Large Size Favored Large Size Favored Directional Selection Average Size Favored Average Size Favored Stabilizing Selection Extreme Size Favored Extreme Size Favored Disruptive Selection Variation reduced over time Variation reduced over time Mean changed over time Mean changed over time Variation becomes polarized Variation becomes polarized Before Selection After Selection Time

13. Types of Selection Stabilizing: eliminates extremesStabilizing: eliminates extremes

14. Stabilizing Selection & Balanced Polymorphism SS SS’ S’S’ Dies of malaria SS Lives and reproduces Dies of sickle-cell anemia Dies of malaria Lives and reproduces Dies of sickle-cell anemia Homozygous Normal Homozygous Defective Heterozygous

15. Types of Selection Disruptive: increases both extremesDisruptive: increases both extremes

16. Types of Selection Directional: increases one extremeDirectional: increases one extreme

17. Applying Your Knowledge 1.Stabilizing Selection 2.Disruptive Selection 3.Directional Selection Which type of selection has occurred if The background is sandy with dark rocks and snails are found with either dark or light shell colors?The background is sandy with dark rocks and snails are found with either dark or light shell colors? After spraying with malathion, more fruit flies are found to be resistant to this insecticide?After spraying with malathion, more fruit flies are found to be resistant to this insecticide?

18. Environmental Influences Abiotic FactorsAbiotic Factors –climate –availability of resources

19. Environmental Influences Biotic FactorsBiotic Factors –competition

20. Environmental Influences Biotic FactorsBiotic Factors –predator-prey relationships Camouflage hides prey

21. Environmental Influences Biotic FactorsBiotic Factors –symbiosis: close interaction between species Parasitism One helped, other harmed

22. Environmental Influences Biotic FactorsBiotic Factors –symbiosis Mutualism Both helped

23. Environmental Influences Biotic FactorsBiotic Factors –symbiosis Commensalism One helped, other neither helped nor harmed

24. Environmental Influences Biotic FactorsBiotic Factors –sexual selection

25. Environmental Influences Biotic FactorsBiotic Factors –altruism and kin selection

26. Applying Your Knowledge 1.Mutualism 2.Commensalism 3.Parasitism Which type of symbiosis is operative if A plant supplies a bee with nectar and the bee takes pollen to other plants of the same species? A plant supplies a bee with nectar and the bee takes pollen to other plants of the same species? Athlete’s foot fungus starts growing between your toes? Athlete’s foot fungus starts growing between your toes?