Ch. 23+24


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  • Bent Grass growing on mine tailings; only individuals tolerant of toxic heavy metals will grow from the seeds blown in from nearby field
  • Bent Grass growing on mine tailings; only individuals tolerant of toxic heavy metals will grow from the seeds blown in from nearby field
  • Every individual has hundreds of mutations 1 in 100,000 bases copied 3 billion bases in human genome But most happen in introns, spacers, junk of various kind Not every mutation has a visible effect. Some effects on subtle. May just affect rate of expression of a gene.
  • 1 family has a lot of children & grandchildren therefore has a greater impact on the genes in the population than other families Genghis Khan tracked through Y chromosome.
  • Small founder group, less genetic diversity than Africans All white people around the world are descended from a small group of ancestors 100,000 years ago (Chinese are white people!)
  • Ch. 23+24

    1. 1. Blue edged slides taken from slide shows by: Kim Foglia Chapter 23- Evolution of populations Chapter 24- Origin of species
    2. 2. 2007-2008 Populations evolve Individuals are selected
    3. 3. REZNICK & ENGLER- (1980’s) Guppy experiments Changes in populations happened within 11 years Age and size at sexual maturity change depending on predators IMAGE FROM Campbell and Reece AP BIOLOGY
    4. 4. <ul><li>Small killifish eat juvenile guppies </li></ul><ul><li>Large pike-cichlids eat adult guppies </li></ul><ul><li>Guppies in populations with pike-cichlid predators </li></ul><ul><li>begin reproducing at a younger age and are smaller </li></ul><ul><li>at maturity than guppies in populations preyed on by </li></ul><ul><li>killifish </li></ul>IMAGE FROM Campbell and Reece AP BIOLOGY
    5. 5. <ul><li>Moving guppies to pools with different predators changes size and age of maturity in population </li></ul><ul><li>Changes are heritable </li></ul>IMAGE FROM Campbell and Reece AP BIOLOGY
    6. 6. Changes in populations 2005-2006 Insecticide resistance Pesticide molecule Insect cell membrane Target site Resistant target site Target site Decreased number of target sites
    7. 7. Fitness <ul><li>Survival & Reproductive success </li></ul><ul><ul><li>individuals with one phenotype leave more surviving offspring </li></ul></ul>Body size & egg laying in water striders
    8. 8. Variation & natural selection <ul><li>Variation is the raw material for natural selection </li></ul><ul><ul><li>there have to be differences within population </li></ul></ul><ul><ul><li>some individuals must be more fit than others </li></ul></ul>
    9. 9. Where does Variation come from? <ul><li>Mutation </li></ul><ul><ul><li>random changes to DNA </li></ul></ul><ul><ul><ul><li>errors in mitosis & meiosis </li></ul></ul></ul><ul><ul><ul><li>environmental damage </li></ul></ul></ul><ul><li>Sex </li></ul><ul><ul><li>mixing of alleles </li></ul></ul><ul><ul><ul><li>recombination of alleles </li></ul></ul></ul><ul><ul><ul><ul><li>new arrangements in every offspring </li></ul></ul></ul></ul><ul><ul><ul><li>new combinations = new phenotypes </li></ul></ul></ul><ul><ul><li>spreads variation </li></ul></ul><ul><ul><ul><li>offspring inherit traits from parent </li></ul></ul></ul>Mean beak depth of parents (mm) Medium ground finch 8 8 9 10 11 9 10 11 1977 1980 1982 1984 Dry year Dry year Dry year Wet year Beak depth Beak depth of offspring (mm)
    10. 10. 5 Agents of evolutionary change Mutation Gene Flow Genetic Drift Selection Non-random mating
    11. 11. 1. Mutation & Variation <ul><li>Mutation creates variation </li></ul><ul><ul><li>new mutations are constantly appearing </li></ul></ul><ul><li>Mutation changes DNA sequence </li></ul><ul><ul><li>changes amino acid sequence? </li></ul></ul><ul><ul><li>changes protein? </li></ul></ul><ul><ul><ul><li>changes structure? </li></ul></ul></ul><ul><ul><ul><li>changes function? </li></ul></ul></ul><ul><ul><li>changes in protein may change phenotype & therefore change fitness </li></ul></ul>
    12. 12. 2. Gene Flow <ul><li>Movement of individuals & alleles in & out of populations </li></ul><ul><ul><li>seed & pollen distribution by wind & insect </li></ul></ul><ul><ul><li>migration of animals </li></ul></ul><ul><ul><ul><li>sub-populations may have different allele frequencies </li></ul></ul></ul><ul><ul><ul><li>causes genetic mixing across regions </li></ul></ul></ul><ul><ul><ul><li>reduce differences between populations </li></ul></ul></ul>
    13. 13. Human evolution today <ul><li>Gene flow in human populations is increasing today </li></ul><ul><ul><li>transferring alleles between populations </li></ul></ul>Are we moving towards a blended world?
    14. 14. 3. Non-random mating <ul><li>Sexual selection </li></ul>
    15. 15. SEXUAL SELECTION <ul><li>Favors traits with no advantage for survival </li></ul><ul><li>other than fact that males/females prefer them </li></ul><ul><li>Leads to pronounced differences between sexes =SEXUAL DIMORPHISM </li></ul>
    16. 16. KIN SELECTION <ul><li>Natural selection that favors altruistic behavior by enhancing reproductive success of relatives </li></ul>Bird that calls to warn others is in danger of being eaten, but does it anyway. Image from:
    17. 17. 4. Genetic drift <ul><li>Effect of chance events </li></ul><ul><ul><li>founder effect </li></ul></ul><ul><ul><ul><li>small group splinters off & starts a new colony </li></ul></ul></ul><ul><ul><li>bottleneck </li></ul></ul><ul><ul><ul><li>some factor (disaster) reduces population to small number & then population recovers & expands again </li></ul></ul></ul>Warbler finch Tree finches Ground finches
    18. 18. Founder effect <ul><li>When a new population is started by only a few individuals </li></ul><ul><ul><li>some rare alleles may be at high frequency; others may be missing </li></ul></ul><ul><ul><li>skew the gene pool of new population </li></ul></ul><ul><ul><ul><li>human populations that started from small group of colonists </li></ul></ul></ul><ul><ul><ul><li>example : colonization of New World </li></ul></ul></ul>
    19. 19. Bottleneck effect <ul><li>When large population is drastically reduced by a disaster </li></ul><ul><ul><li>famine, natural disaster, loss of habitat… </li></ul></ul><ul><ul><li>loss of variation by chance event </li></ul></ul><ul><ul><ul><li>alleles lost from gene pool </li></ul></ul></ul><ul><ul><ul><ul><li>not due to fitness </li></ul></ul></ul></ul><ul><ul><ul><li>narrows the gene pool </li></ul></ul></ul>
    20. 20. Cheetahs <ul><li>All cheetahs share a small number of alleles </li></ul><ul><ul><li>less than 1% diversity </li></ul></ul><ul><ul><li>as if all cheetahs are identical twins </li></ul></ul><ul><li>2 bottlenecks </li></ul><ul><ul><li>10,000 years ago </li></ul></ul><ul><ul><ul><li>Ice Age </li></ul></ul></ul><ul><ul><li>last 100 years </li></ul></ul><ul><ul><ul><li>poaching & loss of habitat </li></ul></ul></ul>
    21. 21. Conservation issues <ul><li>Bottlenecking is an important concept in conservation biology of endangered species </li></ul><ul><ul><li>loss of alleles from gene pool </li></ul></ul><ul><ul><li>reduces variation </li></ul></ul><ul><ul><li>reduces adaptability </li></ul></ul>Breeding programs must consciously outcross Peregrine Falcon Golden Lion Tamarin
    22. 22. 5. Natural selection <ul><li>Differential survival & reproduction due to changing environmental conditions </li></ul><ul><ul><ul><li>climate change </li></ul></ul></ul><ul><ul><ul><li>food source availability </li></ul></ul></ul><ul><ul><ul><li>predators, parasites, diseases </li></ul></ul></ul><ul><ul><ul><li>toxins </li></ul></ul></ul><ul><ul><li>combinations of alleles that provide “ fitness ” increase in the population </li></ul></ul><ul><ul><ul><li>adaptive evolutionary change </li></ul></ul></ul>
    23. 23. POLYGENIC traits are controlled by two or more genes. A bell shaped curve is typical of polygenic traits Graph from BIOLOGY by Miller and Levine; Prentice Hall Publshing ©2006
    24. 24. <ul><li>DIRECTIONAL SELECTION </li></ul>Graph from BIOLOGY by Miller and Levine; Prentice Hall Publshing©2006 Individuals at one end of the curve have higher fitness than individuals in middle or at other end. Graph shifts as some individuals fail to survive at one end and succeed and reproduce at other Low mortality, high fitness High mortality, low fitness KEY Food becomes scarce.
    25. 25. Beak size varies in a population Birds with bigger beaks can feed more easily on harder, thicker shelled seeds. A food shortage causes small and medium size seeds to run low. Birds with bigger beaks would be selected for and increase in numbers in population. EXAMPLE OF DIRECTIONAL SELECTION
    26. 26. <ul><li>STABILIZING SELECTION </li></ul>Graph from BIOLOGY by Miller and Levine; Prentice Hall Publshing©2006 Individuals in center of the curve have higher fitness than individuals at either end Graph stays in same place but narrows as more organisms in middle are produced.
    27. 27. Key Percentage of Population Brightness of Feather Color Selection against both extremes keep curve narrow and in same place. Section 16-2 Low mortality, high fitness High mortality, low fitness Stabilizing Selection Male birds use their plumage to attract mates. Male birds with less brilliant and showy plumage are less likely to attract a mate Male birds with showy plumage are more likely to attract a mate. Male birds with showier, brightly colored plumage also attract predators, and are less likely to live long enough to find a mate. The most fit is male bird in the middle-- showy, but not too showy . STABILIZING SELECTION Graph from BIOLOGY by Miller and Levine; Prentice Hall Publshing©2006
    28. 28. Human babies born with low birth weight are less likely to survive. Babies born too large have difficulty being born. Average size babies are selected for. EXAMPLE OF STABILIZING SELECTION
    29. 29. <ul><li>DISRUPTIVE SELECTION </li></ul>Graph from BIOLOGY by Miller and Levine; Prentice Hall Publshing©2006 Individuals at extremes of the curve have higher fitness than individuals in middle. Can cause graph to split into two. Selection creates two DIFFERENT PHENOTYPES
    30. 30. A bird population lives in area where climate change causes medium size seeds become scarce while large and small seeds are still plentiful. Birds with bigger or smaller beaks would have greater fitness and the population may split into TWO GROUPS. One that eats small seeds and one that eats large seeds. EXAMPLE OF DISRUPTIVE SELECTION
    31. 32. <ul><li>WHAT IS A SPECIES? </li></ul><ul><li>Defined by Ernst Mayr </li></ul><ul><li>Population whose members can interbreed </li></ul><ul><li>AND produce viable, fertile offspring </li></ul>TWO DISTINCT SPECIES Body and coloration are similar . . . but their songs and other behaviors are different enough to prevent interbreeding
    32. 33. In the wild lions and tigers don’t interbreed but in zoos… can get hybrids LIGER - Male lion X female tiger TIGON- Male tiger X female lion Largest cat in world . . . but male ligers are sterile
    33. 39. Blue Footed Booby dance
    34. 46. Hybrid
    36. 54. CURRENT DEBATE NOT over whether evolution happens … overwhelming evidence here! BUT . . .Does speciation happen gradually OR rapidly in response to environmental change? GRADUALISM Change happens slowly “ Baby steps” over long Periods of time CHARLES DARWIN CHARLES LYELL
    37. 55. PUNCTUATED EQUILIBRIUM Niles Eldredge- Curator American Museum of Natural History Rate of speciation is NOT CONSTANT Rapid change when 1 st split from parent population Unchanging for long periods Stephen Jay Gould (1941-2002) Paleontologist/evolutionary biologist TIME