1. Warm Up 2/22/16 Wk. 5 Why don’t we look exactly like our biological parents even though they provided us with all of our genes?

2. Objective: Students will be able to explain the factors that cause evolution and diversity Students will be able to recognize that new mutations are constantly being generated in a gene pool Students will be able to explain why natural selection acts on phenotype rather than genotype of an organism

3. GENES AND VARIATION EVOLUTION AS GENETIC CHANGE 16-1 & 16-2

4. Darwin in the Dark Darwin had two main gaps in his theory of evolution:  Heritable traits??  Yeah, I see variation. How does it appear? I don’t know!

5. Darwin in the Dark By the 1930s, biologists understood that genes control heritable traits  Changes in genes=heritable variation=emergence of natural selection  Ex: moth color

6. Darwin in the Dark Watson & Crick  Shed light on mutations and genetic variation

7. Remember ? Genes have at least two forms, or alleles. Ex: Flower color

8. Variation and Gene Pools Population: A group of individuals of the same species that interbreed  Ex: # of humans living in NY city

9. Variation and Gene Pools

11. Variation and Gene Pool

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14. Variation and Gene Pools The relative frequency of an allele has NOTHING to do with whether the allele is dominant or recessive In the mouse fur example, the recessive allele occurs more frequently than the dominant allele

15. So How Are Genes and Evolution Related? Evolution is any change in the relative frequency of alleles in a population Back to the mice fur coat example:  If the relative frequency of the B allele (black fur) in the mouse population changed over time from 20% to 30%, the population is evolving!

16. Sources of Genetic Variation 2 main sources of genetic variation:  Mutations  Genetic Shuffling from sexual reproduction

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18. Mutations Any change in a sequence of DNA Why do they occur?  Mistakes in DNA replication  Radiation  Chemicals

19. Mutations Don’t always affect an organism’s phenotype, e.g., not all mutations result in Marvel superheroes! Many mutations do produce changes in phenotype  May affect an organism’s fitness or it may have no affect on fitness

20. Gene Shuffling Bringing together new combinations of genes How?  Meiosis (crossing over, production of gametes)

21. Gene Shuffling Sexual reproduction produces many different phenotypes without changing the relative frequency of alleles in a population How?

22. Gene Shuffling Think of this like a deck of playing cards Shuffling leads to many different hands but does not change the # of kings, queens, aces, etc. in the deck The probability of picking a king from the deck will always be 4/52 no matter how many times you shuffle the deck

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24. Single-Gene and Polygenic Traits The # of phenotypes produced for a given trait depends on how many genes control the trait

25. Single-Gene and Polygenic Traits

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27. Single-Gene and Polygenic Traits

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29. Single-Gene and Polygenic Traits An example of a polygenic trait is height Bell shaped curve

30. Evolution as Genetic Change Why doesn’t natural selection ever act directly on genes?

31. Evolution as Genetic Change It is the entire organism, not a single gene, that either survives and reproduces or dies without reproducing. Natural selection can therefore only affect which individuals survive and reproduce and which do not.

32. Evolution as Genetic Change If an individual produces many offspring its alleles stay in the gene pool and may increase in frequency If individual dies without reproducing, the individual does not contribute its alleles to the population’s gene pool.

33. Celebrities who might not have a chance to contribute their alleles to the population gene pool

34. Natural Selection on Single-Gene Traits Natural selection on single gene traits can lead to changes in allele frequencies and thus to evolution

35. Natural Selection on Single-Gene Traits A population of normally brown lizards experiences mutations that produce red and black forms. The allele frequencies may evolve to favor the allele for black lizards since they can absorb more sunlight and warm up faster on colder days.

36. Natural Selection on Single-Gene Traits The allele frequencies for red lizards will decrease and not be common since they are easier to see by their predators

37. Natural Selection on Polygenic Traits When traits are controlled by more than one gene the effects of natural selection are more complex Remember, multiple alleles on a trait produces a range of phenotypes

38. Natural Selection on Polygenic Traits Polygenic traits produce a range of phenotypes resembling a bell curve

39. Natural Selection on Polygenic Traits The fitness of individuals close to one another on the curve will not be very different The fitness can vary a great deal from one end of such a curve to the other  Where fitness varies, natural selection can act

40. Natural Selection on Polygenic Traits Natural selection can affect the distributions of phenotypes in any of 3 ways:  Directional selection  Stabilizing selection  Disruptive selection

41. Directional Selection

42. Ex: A population of seed eating birds experiences directional selection when a food shortage causes the supply of small seeds to run low (so more large seeds in circulation).

43. Stabilizing Selection

44. Ex: Human babies born at an average mass are more likely to survive than babies born either much smaller (less healthy) or much larger (difficulty being born) than average

45. Disruptive Selection

46. If pressure of natural selection is strong enough and lasts long enough, this situation can cause the single curve to spilt into two  In other words, selection creates two distinct phenotypes

47. Disruptive Selection Ex: Average sized seeds become less common, and larger and smaller seeds become more common. As a result, the bird population splits into two subgroups specializing in eating different sized seeds. Birds with unusually small or large beaks would have higher fitness

48. Question In disruptive selection, organisms on which part of the curve have the lowest fitness?

49. Question How does the curve change in stabilizing selection?

50. Hardy-Weinberg Principle States that allele and genotype frequencies in a population will remain CONSTANT from generation to generation.  In absence of evolutionary change

51. Hardy-Weinberg Principle To achieve genetic equilibrium, five conditions must be met:  1.) Large population  2.) Random mating  3.) No movement in or out of population (no immigration or emigration)  4.) No mutations  5.) No natural selection

52. Hardy-Weinberg Equation First of all, WHYYY is it useful to learn about this equation??  Can be applied to observations for study of population futures.  Shows how prevalent alleles are in a population.

53. Hardy-Weinberg Equation There are two important equations: p + q=1 (Allele freq. equation) p 2 + 2pq + q 2 =1 (Genotype freq. equation)

54. Hardy-Weinberg Equation p + q=1 p= freq. of dominant allele (for example, A) q= freq. of recessive allele (for example, a) 1= total freq. of all alleles in population

55. Hardy-Weinberg Equation p 2 + 2pq + q 2 =1 p 2 = freq. of homozygous dominant genotype (for example, AA) 2pq= freq. of heterozygous genotype (for example, Aa) q 2 = freq. of homozygous recessive genotype (for example, aa)

56. Hardy-Weinberg Equation Get out a sheet of paper Label it “Hardy-Weinberg extended practice” Do the following problem (few minutes) We will discuss afterwards

57. Hardy-Weinberg Problems The allele y occurs with a frequency of 0.8 in a population of clams. Give the frequency of genotypes YY, Yy, and yy. Show your work!

58. Hardy-Weinberg Problems The allele y has a frequency q = 0.8. You know that p + q = 1

59. Hardy-Weinberg Problems Using that equation: p = 1 – 0.8 = 0.2. Now you can estimate the frequency of each genotype using your p and q:  YY genotype frequency = p 2 = 0.04  Yy genotype frequency = 2pq = 0.32  yy genotype frequency = q 2 = 0.64.

60. Hardy-Weinberg Problems A population of aliens may be blue (the dominant phenotype) or green (the recessive phenotype). Blue aliens have the genotype BB or Bb. Green aliens have the genotype bb. The frequency of the BB genotype is.50. What is the frequency of the B allele?

61. Hardy-Weinberg Problems Frequency of the BB genotype is.50 (given). Using the equation p 2 + 2pq + q 2 =1 we know that p 2 is the homozygous dominant genotype.  So: p 2 =.50

62. Hardy-Weinberg Problems To find the frequency of the B allele (p) we need to take the square root of p 2 and.50 from the equation p 2 =.50 The result is then p=.707=freq. of B allele!

63. Hardy-Weinberg Problems In the same problem, what is the frequency of heterozygous aliens? (In other words what is 2pq) We know:  p 2 =.50 (given)  p=.707 (solved on last slide)

64. Hardy-Weinberg Problems To answer the question, we first need to find q (so we can solve for 2pq). Remember, p + q=1 So,.707 + q=1 q=.293 Now that we know q, we can determine the frequency of heterozygous aliens (2pq) 2(p)(q)=2(.707)(.293)=.414=freq. of heterozygous aliens

65. Overwhelmed? PowerPoint posted on website Hardy-Weinberg worksheet problems 1-3 with answers posted on website Use as study tool for Friday’s quiz!