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The Evolution of Populations and the Origin of Species

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The Evolution of Populations and the Origin of Species

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  1. The Evolution of Populations and the Origin of Species Chapters 23-24

  2. Evolution happens to populations/ species over time. • Lamarckian evolution - evolution result of change in individual in response to environment (i.e. giraffe stretching its neck to eat) - incorrect hypothesis.

  3. http://necsi.org/projects/evolution/lamarck/lamarck/giraffes.jpghttp://necsi.org/projects/evolution/lamarck/lamarck/giraffes.jpg

  4. Population composed of many different genotypes, phenotypes because of alleles carried in population. • Sum total of all alleles in population - gene pool; variation in gene pool - variations in individual phenotypes.

  5. http://www.brooklyn.cuny.edu/bc/ahp/LAD/C21/graphics/C21_GenePool_2.GIFhttp://www.brooklyn.cuny.edu/bc/ahp/LAD/C21/graphics/C21_GenePool_2.GIF

  6. Measure of genetic variation in population - allele frequency of gene. • # of copies of allele divided by total # of copies of gene in population.

  7. http://anthro.palomar.edu/vary/images/map_of_A_blood_allele.gifhttp://anthro.palomar.edu/vary/images/map_of_A_blood_allele.gif

  8. http://www.uni-kiel.de/medinfo/mitarbeiter/krawczak/folien/vorlesung2/img002.jpghttp://www.uni-kiel.de/medinfo/mitarbeiter/krawczak/folien/vorlesung2/img002.jpg

  9. If population does not change - Hardy-Weinberg equilibrium – no evolution. • Frequencies change - evolution occurring.

  10. http://www.southtexascollege.edu/crj/human%20evolution.jpg

  11. Conditions for population to stay at Hardy-Weinberg equilibrium: • 1Random mating occurs. • 2Population large enough to avoid random statistical fluctuations in frequencies. • 3No mutation.

  12. http://w3.dwm.ks.edu.tw/bio/activelearner/18/images/ch18c2.jpghttp://w3.dwm.ks.edu.tw/bio/activelearner/18/images/ch18c2.jpg

  13. 4No migration into/out of population. • 5No natural selection. • Under conditions - free flow of genes between members of same species. • Alleles shuffled up from 1 generation to next.

  14. http://www.artgame.com/images3/migration.jpg

  15. In wildflower population of 500, 80% (0.8) of flower color alleles are R and 20% (0.2) are r. • Each gamete - 1 allele for flower color; gamete drawn from gene pool at random has 0.8 chance of bearing R allele, 0.2 chance of bearing r allele.

  16. http://k43.pbase.com/u29/gaocus/upload/17965482.wildflower.jpghttp://k43.pbase.com/u29/gaocus/upload/17965482.wildflower.jpg

  17. Rule of multiplication - frequencies of 3 possible genotypes in next generation. • RR genotype - probability of picking 2 R alleles is 0.64 (0.8 x 0.8 = 0.64 or 64%). • rr genotype - probability of picking 2 r alleles is 0.04 (0.2 x 0.2 = 0.04 or 4%).

  18. Heterozygous individuals - either Rr or rR - R allele from sperm or egg. • Probability of ending up with both alleles is 0.32 (0.8 x 0.2 = 0.16 for Rr, 0.2 x 0.8 = 0.16 for rR, and 0.16 + 0.16 = 0.32 or 32% for Rr + rR).

  19. p = gene frequency of dominant allele, q = frequency of recessive allele; p + q = 1. • Equation for Hardy-Weinberg principle is: • p2 + 2pq + q2 = 1 • 2pq - # heterozygotes in population.

  20. http://bill.srnr.arizona.edu/classes/182/GeneFreqs/HardyWeinberg-lg.jpeghttp://bill.srnr.arizona.edu/classes/182/GeneFreqs/HardyWeinberg-lg.jpeg

  21. Hardy-Weinberg equilibrium, frequency of dominant homozygous curly hair (CC) is 64%. Percentage with curly hair? • p = frequency dominant allele (C) q frequency recessive allele (c).

  22. CC frequency 64% so p2 = .64; p = .8. • (p + q = 1) q = 1 - .8 = 2. • Individual with curly hair - either CC or Cc. • Percentage of population with curly hair is p2 + 2pq = .64 + 2(.8*.2) = .96 or 96% of population.

  23. Instabilities in populations • Conditions can change Hardy-Weinberg equilibrium. • Mutations cannot happen in equilibrium; occurs in real world. • Errors in DNA replication accumulate over time as well as mutagenic factors in environment. • Mutations can lead to new alleles not previously in gene pool.

  24. http://www.sciencemuseum.org.uk/exhibitions/genes/images/1-3-5-1-2-2-2-2-2-0-0.jpghttp://www.sciencemuseum.org.uk/exhibitions/genes/images/1-3-5-1-2-2-2-2-2-0-0.jpg

  25. Mutations either neutral or harmful on survival of individual. • New phenotypes in population raw material that natural selection acts on to drive evolution; mutations only source of new alleles. • Migration affects equilibrium. • Different populations have different allelic frequencies in gene pools.

  26. http://www.geo.arizona.edu/Antevs/nats104/00lect26humigrout.jpghttp://www.geo.arizona.edu/Antevs/nats104/00lect26humigrout.jpg

  27. 1 population breeds with another population, frequencies of alleles change (gene flow). • Small population more likely to have random event than large population.

  28. http://web.pdx.edu/~mfish/image019.jpg

  29. Genetic drift - changes in allele frequencies in small population caused by random events. • Even in large population if small # of individuals pass on traits can decrease diversity. • Individuals that do not pass traits on may have harmful alleles - alters gene pool of next generation (2 ways)

  30. 1Bottleneck - large population reduced to small # by disease, natural disaster, over-hunting/fishing. • Individuals left eventually reproduce, generations not representative of original gene pool.

  31. Inbreeding usually follows bottleneck; individuals with same recessive genes have more chance of passing harmful gene on. • Population more susceptible to disease/infections that may not have occurred with more diversity in population.

  32. http://www.brooklyn.cuny.edu/bc/ahp/LAD/C21/graphics/C21_Bottleneck_2.GIFhttp://www.brooklyn.cuny.edu/bc/ahp/LAD/C21/graphics/C21_Bottleneck_2.GIF

  33. 2Founder effect - small # of individuals of species migrate into new habitat. • If only a few individuals colonize new area, new population reflect only their gene pool not larger gene pool where they came from.

  34. http://www.answersingenesis.org/creation/images/v18/i3/p13_step3.JPGhttp://www.answersingenesis.org/creation/images/v18/i3/p13_step3.JPG

  35. Nonrandom mating - equilibrium cannot occur. • Individuals must choose mate randomly without respect to phenotype. • If phenotype influences selection, genotypes and phenotypes of population will be changed.

  36. http://bioweb.wku.edu/courses/Biol430/wsquirrelHR.jpg

  37. Self-fertilization in plants has this effect. • Reduces # of heterozygotes in population; increases # of homozygotes. • Many species exhibit sexual selection (form of nonrandom mating)

  38. http://www015.upp.so-net.ne.jp/shuri/shuri_study/what_is_si.GIFhttp://www015.upp.so-net.ne.jp/shuri/shuri_study/what_is_si.GIF

  39. Natural selection - differential production of offspring based on inherited traits. • Individuals with more favorable phenotypes may survive, reproduce; alters population frequencies. • Fitness - key description of natural selection.

  40. http://www.telomere.org/images/Sloth.jpg

  41. Fitness - organism’s ability to contribute alleles, traits to future generations. • Factors involved - ability to survive to reproductive age, mate and produce offspring, raise offspring to maturity. • Other factors - ability to escape predation, gather food, attract mates, or care provided to offspring.

  42. http://www.agpix.com/catalog/AGPix_CoTo11/large/AGPix_CoTo11_0092_Lg.jpghttp://www.agpix.com/catalog/AGPix_CoTo11/large/AGPix_CoTo11_0092_Lg.jpg

  43. Individual with long life but few offspring - poor fitness if other individuals have more offspring. • Animals that take care of offspring - greater fitness than those that do not. • Balanced by having more offspring that receive little care/fewer offspring that receive more care.

  44. http://www.facstaff.bucknell.edu/ddearbor/BFAL_feeds.jpg

  45. Three types of selective pressures that affect natural selection over time. • Any given population, trait distribution bell-shaped.

  46. http://www.csulb.edu/~kmacd/346NotesI_files/normalCurve.gif

  47. 1Stabilizing selection - not change average, tends to sharpen curve. • Newborns can have problems if too large or too small at birth – stabilizing selection pushed average to 8 pounds; perfect size for newborn infant.