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Population genetics as a means to explore

Charles Darwin (1809-1882). ALFRED WALLACE ( 1823-1913 ). Population genetics as a means to explore. EVOLUTION. A. Theory of Evolution. Around world, many people held view that each species came about by divine (godly) creation

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Population genetics as a means to explore

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  1. Charles Darwin(1809-1882) • ALFRED WALLACE(1823-1913) Population genetics as a means to explore EVOLUTION

  2. A. Theory of Evolution • Around world, many people held view that each species came about by divine (godly) creation • Buddhism: 1. who cares?; 2. spiritual beings take many forms including man in each cycle • Hinduism: 1. primal man Purusa sacrificed to become universe - head became heavens, arms became warriors, legs the commoners, feet the serfs; 2. Vishnu commanded servant Brahma to create world which he did out of lotus flower • Islam: Allah (God) created heaven and earth in 6 days (Quran 7:54) • Judeo-Christian: God created each creature including man in 6 days (Genesis I:20-25)

  3. During 19th century, many fossils discovered of species not currently in existence • Question of origin spawned many hypotheses • 1831 voyage of amateur naturalist Charles Darwin along with 1854 exploration of naturalist Alfred Wallace gave enough evidence for both to propose theory of evolution of populations of organisms via natural selection

  4. Poor Mr. Wallace

  5. B. Natural Selection • Process that results in survival and propagation of organisms with favorable mutations that are better suited to adapt to environment than those without • Nature selects adaptations of organisms best suited to succeed in environment (“survival of the fittest”) • Acts on phenotype of individual – whatever physical appearance or expression of trait to help it to survive and reproduce (homozygous or heterozygous genotype is not important) • Best phenotype of population will dominate

  6. What makes one mutation good vs. bad? Nature! Detrimental Mutation Beneficial Mutation Mutations will always happen. Some are good, some are bad, most are neutral. No longer referred to as “mutations” but rather “adaptations”

  7. Darwin’s Finch Evolution

  8. Two types of adaptations: • Structural – physical changes in appearance • Physiological – change in how organism functions or metabolizes (making venom, digesting cow milk)

  9. Structural Adaptations Thorns made it harder for predators to eat rosebuds White coat helps it blend in, making it easier to stalk prey

  10. Structural Adaptations Pouch enables joey to be protected but lets mom still roam around to find food Opposable thumbs makes it easier to grasp small objects with one hand while leaving other hand free for defense. .

  11. Evidence of natural selection is of peppered moths in industrial age England via “industrial melanism” • Prior to industrial revolution, 98% of peppered moths were light colored to blend in with light colored tree bark 98% 2% carbonaria typica

  12. After industry & soot from factories turned tree trunks black, those dark peppered moths had an advantage and soon became most common 98% 2%

  13. 3 different types of natural selection that act on structural variations: • Stabilizing selection • Directional selection • Disruptive selection

  14. STABILIZING SELECTION • Stabilizing Selection: natural selection that favors AVERAGE individuals in a population • In spider population, average size is a survival advantage. Why? • Smaller spider may find it hard to find food (too weak or food is too big) • Bigger spider may not find enough food to survive, or predators like birds, can see them now and eat them • In this case, the average spider is at an advantage so gets “selected for”

  15. Selection for average size for particular spider species 400 Number of Spiders 300 200 100 3.5 cm 4.5 cm 5.5 cm 6.5 cm 7.5 cm 0.5 cm 2.5 cm 1.5 cm Size of Spiders • Shape of bell curve shows selection of the middle or average type of spiders • In humans, nature favors medium heights (polygenic inheritance) Normal variation (for particular spider species)

  16. DIRECTIONAL SELECTION • Directional selection: natural selection favors ONE of the EXTREME variations of a trait • In hummingbird population, suppose that particular flower has lots of nectar for the taking, but the flower is very long , so only hummingbirds with very long beaks will be able to get at it

  17. those hummingbirds with EXTREMELY long beaks will be favored in this region where these flowers grow and will be “selected for” by nature • average-sized or small beaks will be at a disadvantage since their beaks can’t reach the nectar

  18. Normal variation Selection for longer beaks 5 3 4 7 2 6 8 9 10 11 1 Directional Selection Number of Hummingbirds Beak Size (cm) • Shape of this curve shows the selection for the EXTREME length (~8 cm)

  19. DISRUPTIVE SELECTION • Disruptive Selection: natural selection favors BOTH EXTREME variations for a particular trait • In the snail-like marine organism called a limpet, shell colors range from white, to tan, to dark brown • adults attach onto rocks which are either light or dark colored – there is no medium (intermediate) colored rocks in this environment • birds eat limpets – if they see them

  20. white limpets will have advantage on light rocks due to camouflage • dark limpets will have advantage on dark rocks or the same reason • tan or medium colored limpets will be at a disadvantage since there are no rocks to camouflage them

  21. Shape of this curve shows selection for both of the extreme colors Intermediate (tan) variation Extreme (white) variation Extreme (dark) variation Number of limpets

  22. C. Changes in Gene Pool • All alleles in population are considered gene pool • Only these alleles can make new organisms • Ex: If mom & dad are homozygous dominant for brown eyes, blue eyes just aren’t in your gene pool • Numerical count of alleles in specific population called allelic frequency • What is allelic frequency of B & b in this gene pool? TOTAL: 14 alleles (7 pigs) B: 7/14 = 50% b: 7/14 = 50%

  23. CHANGE in ALLELIC FREQUENCY = EVOLUTION! G = 9/12 G = 17/24 B = 3/12 B = 7/24

  24. If gene pool has large variety of alleles, it’s considered genetically diverse • High biodiversity is important in health & survival of population against: • Disease • Natural disasters • Loss of habitat • Irish Potato Famine (1845-1852) is direct result of lack of genetically diverse potatoes succumbing to mold infestation

  25. Irish Potato Famine 1845-1852 • Potatoes originated from Andes Mountains in S. America – many different varieties of potatoes • Only few varieties made it to Ireland, where poor farmers would grow it as mainstay of food • “Potato blight” fungal disease of potato crops carried on ships landed in Ireland in 1844 destroying entire crops • Mass starvation, disease, emigration led to 20-25% drop in population of Ireland

  26. How does an organism acquire diversity? • Mutations! • Beneficial - improved survival • Neutral – doesn’t improve or harm survival • Lethal – would kill organism

  27. If allele is lethal (as in t in Tay-Sachs), will only be passed down if it doesn’t affect heterozygote • Tt is completely healthy, will live to reproduce • tt will die before reproducing • Exceptions are H dominant allele in Huntington’s where individual reproduces before lethality of allele manifests

  28. Are we in danger of famine due to lack of diversity? • Corn • Chickens • Soybeans A new study (2008) has found that commercial birds raised for eggs and meat are missing more than half of the genetic diversity found in native chickens, possibly increasing a vulnerability to new diseases and raising serious questions about the sustainability of the poultry industry. Many different varieties of soy, although we only grow one

  29. Without diversity, organism is vulnerable to disease and at risk of extinction Passenger Pigeon N. America 1914 Dodo Mauritania, 1681 Golden Toad Costa Rica 1989

  30. Hardy-Weinberg Principle • To see if evolution is occurring, there must be a change in allele frequency • An equation called the Hardy-Weinberg equation is a mathematical way to determine if change is happening • p2 + 2pq +q2 = 1.0 • p = numbers of dominant alleles • q = numbers of recessive alleles • As long as equation = 1.0, no evolution • If equation  1.0, change is happening = evolution

  31. H-W Sample Problem • Ex: Within a population of butterflies, the color brown (B) is dominant over the color white (b). And, 40% of all butterflies are white. Given this simple information calculate the following: • A. percentage of butterflies in the population that are heterozygous (Bb). • B. frequency of homozygous dominant individuals (BB). • Remember, p = B, q = b • What is 2pq? • What is p2?

  32. Equation: p2 +2pq +q2 = 1.0; p + q = 1.0 • White (recessive) = bb = 40% • then bb = q2 = 0.4 • q = 0.4 = 0.632 (i.e. 0.632 x 0.632 = 0.4) • q = 0.63 • Since p + q = 1.0, p = 1.0 - 0.63 = 0.37 • p = 0.37 • A. heterozygous? • 2pq = 2 [(0.37)(0.63)] = 0.47 • B. homozygous dominant? • BB = p2 or (0.37)2 = 0.14 Extra Credit on Test/Quiz

  33. D. Evidence for Evolution • Direct evidence for evolution (via drug-resistant bacteria & different plant species) makes it easy to see evolution exists in lower-order species • Evidence for evolution in the higher-order species (animals & humans) is more indirect: • Fossils:bone structures are similar but act differently • Anatomy: looking at bones of different species tells us certain bones do identical things • Embryology: species that are way different as adults (humans vs. chickens) look identical when embryos • Biochemistry: DNA or RNA differences between species is good comparison (chimps & humans 98% identical)

  34. Fossils • Important pieces of evidence for evolution because it provides record of early life and evolutionary history • Paleontologists gathered evidence of whale’s ancestors and believe they were land-dwelling, dog-like animals Whale still has mammalian HIP BONES!

  35. Anatomy • Can compare two or more different species and see they have structural features in common which are called homologous structures

  36. Embryology • Evidence of same structure in embryonic stage tells us that all have common, albeit distant, ancestor • Embryo: earliest stage of growth and development of both plants and animals • All fish, reptile, bird, and mammal embryos have tails and gill slits (no air in uterus)

  37. Biochemistry • Looking at DNA and RNA of individuals and species gives us biochemical evidence for evolution • look at sequence of mitochondrial DNA and RNA to see who’s related to whom

  38. End! Quiz on this section Monday, April 8

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