2. AP Biology 2006-2007 Ch. 22 - Evolution by Natural Selection

3. AP Biology This is not just a process of the past… It is all around us today Artificial selection

4. AP Biology Selective breeding the raw genetic material (variation) is hidden there

5. AP Biology Selective breeding Hidden variation can be exposed through selection!

6. AP Biology In historical context  Other people’s ideas paved the path for Darwin’s thinking competition: struggle for survival population growth exceeds food supply land masses change over immeasurable time

7. AP Biology A Reluctant Revolutionary  Returned to England in 1836  wrote papers describing his collections & observations  long treatise on barnacles  draft of his theory of species formation in 1844  instructed his wife to publish this essay upon his death  reluctant to publish but didn’t want ideas to die with him

8. AP Biology And then came the letter…. Alfred Russel Wallace a young naturalist working in the East Indies, had written a short paper with a new idea. He asked Darwin to evaluate his ideas and pass it along for publication. Then, in 1858, Darwin received a letter that changed everything…

9. AP Biology The time was ripe for the idea! Your words have come true with a vengeance… I never saw a more striking coincidence…so all my originality, whatever it may amount to, will be smashed. To Lyell—

10. AP Biology Voyage: 1831-1836 November 24, 1859, Darwin published “On the Origin of Species by Means of Natural Selection”

11. AP Biology Essence of Darwin’s ideas  Natural selection  variation exists in populations  over-production of offspring  more offspring than the environment can support  competition  for food, mates, nesting sites, escape predators  differential survival  successful traits = adaptations  differential reproduction  adaptations become more common in population

12. AP Biology LaMarckian vs. Darwinian view  LaMarck  in reaching higher vegetation giraffes stretch their necks & transmits the acquired longer neck to offspring  Darwin  giraffes born with longer necks survive better & leave more offspring who inherit their long necks

13. AP Biology Take out the sheets from Yesterday – complete!

14. AP Biology 2006-2007 Slide & Image Storage

15. AP Biology Living creatures have changed Earth’s environment, making other life possible Life has changed over time & in turn has changed the Earth

16. AP Biology Evolution as Change Over Time Evolution! idea accepted before Darwin Evolution!

17. AP Biology Galapagos Recent volcanic origin most of animal species on the Galápagos live nowhere else in world, but they resemble species living on South American mainland. 500 miles west of mainland

18. AP Biology

19. 2006-2007 "Nothing in biology makes sense except in the light of evolution." -- Theodosius Dobzhansky March 1973 Geneticist, Columbia University (1900-1975) Coherent explanation of observations

20. AP Biology (5) Over long periods of time, and given a steady input of new variation into a population, these processes lead to the emergence of new species Essence of Darwin’s ideas (1)Variation exists in natural populations (2) Many more offspring are born each season than can possibly survive to maturity (3) As a result, there is a struggle for existence - competition - competition (4) Characteristics beneficial in the struggle for existence will tend to become more common in the population, changing the average characteristics of the population - adaptations - adaptations

21. AP Biology Stick your neck out… Ask Questions!

22. AP Biology The Birds…  Galápagos birds  22 of the 29 species of birds on the Galapagos are endemic  found only on these islands  collected specimens of all  One particular group…  at first, he paid little attention to a series of small birds  some were woodpecker- like, some warbler-like, & some finch-like

23. AP Biology Darwin’s finches Large-seed eater?Small-seed eater? Warbler?Leaf-browser? Finch?Sparrow? Warbler? Wren?  Darwin was amazed to find out they were all finches  14 species  but only one species on South American mainland  500 miles away  all the birds had to originally come from mainland species How did one species of finches become so many different ones now?

24. AP Biology 2006-2007 Measuring Evolution of Populations

25. AP Biology 5 Agents of evolutionary change MutationGene Flow Genetic DriftSelection Non-random mating

26. AP Biology Populations & gene pools  Concepts  a population is a localized group of interbreeding individuals  gene pool is collection of alleles in the population  remember difference between alleles & genes!  allele frequency is how common is that allele in the population  how many A vs. a in whole population

27. AP Biology Evolution of populations  Evolution = change in allele frequencies in a population  hypothetical: what conditions would cause allele frequencies to not change?  non-evolving population REMOVE all agents of evolutionary change 1. very large population size (no genetic drift) 2. no migration (no gene flow in or out) 3. no mutation (no genetic change) 4. random mating (no sexual selection) 5. no natural selection (everyone is equally fit)

28. AP Biology Hardy-Weinberg equilibrium  Hypothetical, non-evolving population  preserves allele frequencies  Serves as a model (null hypothesis)  natural populations rarely in H-W equilibrium  useful model to measure if forces are acting on a population  measuring evolutionary change W. Weinberg physician G.H. Hardy mathematician

29. AP Biology Hardy-Weinberg theorem  Counting Alleles  assume 2 alleles = B, b  frequency of dominant allele (B) = p  frequency of recessive allele (b) = q  frequencies must add to 1 (100%), so: p + q = 1 bbBbBB

30. AP Biology Hardy-Weinberg theorem  Counting Individuals  frequency of homozygous dominant: p x p = p 2  frequency of homozygous recessive: q x q = q 2  frequency of heterozygotes: (p x q) + (q x p) = 2pq  frequencies of all individuals must add to 1 (100%), so: p 2 + 2pq + q 2 = 1 bbBbBB

31. AP Biology H-W formulas  Alleles:p + q = 1  Individuals:p 2 + 2pq + q 2 = 1 bbBbBB BbBbbb

32. AP Biology What are the genotype frequencies? Using Hardy-Weinberg equation q 2 (bb): 16/100 =.16 0.4 q (b): √.16 = 0.4 0.6 p (B): 1 - 0.4 = 0.6 q 2 (bb): 16/100 =.16 0.4 q (b): √.16 = 0.4 0.6 p (B): 1 - 0.4 = 0.6 population: 100 cats 84 black, 16 white How many of each genotype? population: 100 cats 84 black, 16 white How many of each genotype? bbBbBB p 2 =.36 2pq=.48 q 2 =.16 Must assume population is in H-W equilibrium!

33. AP Biology Using Hardy-Weinberg equation bbBbBB p 2 =.36 2pq=.48 q 2 =.16 Assuming H-W equilibrium Sampled data bbBbBB p 2 =.74 2pq=.10 q 2 =.16 How do you explain the data? p 2 =.20 2pq=.64 q 2 =.16 How do you explain the data? Null hypothesis

34. AP Biology Application of H-W principle  Sickle cell anemia  inherit a mutation in gene coding for hemoglobin  oxygen-carrying blood protein  recessive allele = H s H s  normal allele = H b  low oxygen levels causes RBC to sickle  breakdown of RBC  clogging small blood vessels  damage to organs  often lethal

35. AP Biology Sickle cell frequency  High frequency of heterozygotes  1 in 5 in Central Africans = H b H s  unusual for allele with severe detrimental effects in homozygotes  1 in 100 = H s H s  usually die before reproductive age Why is the H s allele maintained at such high levels in African populations? Suggests some selective advantage of being heterozygous…

36. AP Biology Malaria Single-celled eukaryote parasite (Plasmodium) spends part of its life cycle in red blood cells 1 2 3

37. AP Biology Heterozygote Advantage  In tropical Africa, where malaria is common:  homozygous dominant (normal)  die or reduced reproduction from malaria: H b H b  homozygous recessive  die or reduced reproduction from sickle cell anemia: H s H s  heterozygote carriers are relatively free of both: H b H s  survive & reproduce more, more common in population Hypothesis: In malaria-infected cells, the O 2 level is lowered enough to cause sickling which kills the cell & destroys the parasite. Hypothesis: In malaria-infected cells, the O 2 level is lowered enough to cause sickling which kills the cell & destroys the parasite. Frequency of sickle cell allele & distribution of malaria