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MEASURING EVOLUTION

MEASURING EVOLUTION. When is it Called Evolution?. Microevolution : Changing Allele Frequencies in Populations. Macroevolution : Speciation. Let’s ask an important question:. Can Reebops evolve?. Why do you think they could or could not?

iliana-herring
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MEASURING EVOLUTION

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  1. MEASURING EVOLUTION

  2. When is it Called Evolution? Microevolution: Changing Allele Frequencies in Populations Macroevolution: Speciation

  3. Let’s ask an important question:

  4. Can Reebops evolve? Why do you think they could or could not? What are some of the conditions that might cause Reebops to evolve? How would you know if they did evolve? Write questions and answers in your notebook/ Pair/Share

  5. Consider the Scenario • A drought has forced the Reebop population to move to a new location • The vegetation in this new location is not as tall as in their old location • The tails of straight-tailed Reebops stick up above the vegetation making them more visible to predators (uh-oh) • All straight-tailed Reebops are eaten before they can reproduce.

  6. ASICS MOUNTAINS AVIA DESERT PLANTAR GORGE NEW BALANCE RIVER BROOKS MEADOW TENDONITIS MEADOW KEDS LAKE ADIDAS SWAMP REEBOP COUNTRY NIKE WOODS

  7. How Can We Find out if Reebops Evolve Under These Selection Pressures? • Set up a scientific inquiry. • Gather data • Interpret data

  8. What data/information do we need to answer our question? The answer is in the definition of EVOLUTION EVOLUTION: A process that occurs over many generations that results in heritable changes in a population. Heritable changes = Gene/allele frequency

  9. How Can We Measure Whether Evolution Has Occurred in Reebops? • Look at changes in gene frequency • Remember the Reebops • tail alleles = T (curly), t (straight) • Parents were heterozygous (Tt) for this gene • What percentage of parent gene pool was “T” • What percentage of parent gene pool was “t”

  10. Set up our scientific inquiry • What does gene pool look like after 1 generation without any natural selection? • What does gene pool look like after 1 generation in the low vegetation habitat? • Is there a control group here??? • How can this information tell us if natural selection has occurred?

  11. T t TT Tt T t Tt tt Use our Punnett Square to tell us about gene frequencies after 1 generation Parents: Tt x Tt 100 offspring 25 TT offspring 50Tt offspring 25 tt offspring % T allele? % t allele?

  12. Allele Frequency of parents: 50% T 50% t Allele Frequency after 1 generation: 50 % T 50% t Was there a change in allele frequency? Did evolution occur in our population with out selection?

  13. Now it’s your turn: Do the Natural Selection Experiment with Reebops (a 5 generation experiment)

  14. Did Evolution Occur 5 Generations After the Reebops Moved? • What was the allele frequency for T? • What was the allele frequency for t? • How do they compare to the parent allele frequency?

  15. Sample DataDid Our Reebop Population Evolve?

  16. T(.5) T(.73) t(.5) t(.27) TT TT Tt Tt T(.73) T(.5) t(.5) t(.27 tt tt Tt Tt Use our Punnett Square to tell us about gene frequencies after 5 generations TT = (.5 x .5) = .25 Tt = 2(.5 x .5) = .5 tt = (.5 x .5) = .25 TT = (.73 x .73) = Tt = 2(.73 x .27) = tt = (.27 x .27) = .

  17. Think About This • If selection pressure against tt (straight tail ) continues, will the t allele ever disappear from the population? • If there is no selection pressure against Tt, will the t allele disappear from the population or persist? Write questions and answers in your notebook/ Pair/Share

  18. Natural Selection Doesn’t Always “Select” the Same Way (3 Types of Natural Selection)

  19. 3 Types of Natural Selection • Directional • Disruptive • Stabilizing

  20. Directional Selection Define Reebop tails Kinds of Natural Selection acting on define genetic variability in populations. # organisms # organisms # organisms trait 1 1 5 5 7 7 9 9 11 11 Straight Curly START WITH:

  21. Disruptive Selection Define Tell the guppy story Kinds of Natural Selection acting on define genetic variability in populations. # organisms # organisms trait 1 5 7 9 11 START WITH:

  22. John Endler’s Guppies • Guppy populations in Trinidad. • He found that: • male guppy colors range from brightly colored to drably colored • Male guppies in streams with few predators are brightly colored, but in streams with many predators, they are drably colored like gravel. • females prefer brightly colored males.

  23. Disruptive Selection Define Tell the guppy story Kinds of Natural Selection acting on define genetic variability in populations. # organisms # organisms # organisms trait 1 1 5 5 7 7 9 9 11 11 bright drab START WITH:

  24. Stabilizing Selection Define Human birth weight Kinds of Natural Selection acting on define genetic variability in populations. # organisms # organisms trait 1 5 7 9 11 START WITH:

  25. Human Babies and Birth Weight

  26. Stabilizing Selection Define Human birth weight Kinds of Natural Selection acting on define genetic variability in populations. # organisms # organisms # organisms trait 1 1 5 5 7 7 9 9 11 11 Birth Weight START WITH:

  27. Are There Other Ways to Alter Gene Frequency in a Population? (In Addition to Natural Selection)

  28. Mutation Genetic drift Non-random mating Migration (genetic acquisition and loss) Other Ways to Alter Gene Frequency in a Population

  29. Mutation Positive/negative/neutral mutations Other Ways to Alter Gene Frequency in a Population

  30. Higher organisms Mutation Positive/negative/neutral mutations Point mutations Substitutions/Insertions/Deletions NORMAL SUBSTITUTION INSERTION DELETION What causes gene variability in populations of higher organisms?

  31. Higher organisms Mutation Positive/negative/neutral mutations Point mutations Substitutions/Insertions/Deletions Gene transposition Individual genes Chromosomal rearrangement Other Ways to Alter Gene Frequency in a Population

  32. Mutation Genetic drift Bottleneck Other Ways to Alter Gene Frequency in a Population

  33. Bottleneck Effect Example: North American Seal population

  34. A Story About Reebops and the Bottleneck Effect • Reebops have only one predator, the Ruffledog. These animals are especially fond of straight-tailed Reebops because they are soooo tender. Each year 50 % of the straight-tailed Reebops are lost to Ruffledogs • Remember Straight tail=homozygous; tt RUFFLEDOG

  35. REEBOPS 1998 Population = 200 50 straight-tailed Reebops Lose 50% straight-tailed Reebops to Ruffledog ? animals lost; ? remain REEBOPS 2004 Famine in the new millenium Population = 12 3 straight-tailed Reebops Lose 50% straight-tailed Reebops to Ruffledog ? lost; ? remains 1.5 1.5 25 25 PROBLEMS

  36. Review Bottleneck Effect Which color might represent the straight-tailed Reeboks???? How does this cause genetic drift?

  37. Higher organisms Mutation Genetic drift Bottleneck effect Founder effect Other Ways to Alter Gene Frequency in a Population

  38. Associated with: Small number sets up community in a new region Isolated population Inbreeding in population Example: Ellis van Creveld syndrome in Amish community Founder Effect

  39. Higher organisms Mutation Genetic drift Non-random mating Other Ways to Alter Gene Frequency in a Population

  40. Higher organisms Mutation Genetic drift Non-random mating Migration (allele acquisition and loss) Other Ways to Alter Gene Frequency in a Population

  41. Pick one mechanism of gene variability and write a story about the Reebops ASICS MOUNTAINS AVIA DESERT PLANTAR GORGE NEW BALANCE RIVER BROOKS MEADOW TENDONITIS MEADOW KEDS LAKE ADIDAS SWAMP REEBOP COUNTRY NIKE WOODS Think/Write/Pair/Share

  42. When is it Called Evolution?How do we know if these events cause evolution? (Hint: Hardy Weinberg Equilibrium Equation)

  43. Hardy-Weinberg Law • Godfrey Hardy, Wilheim Weinberg • This law describes a population that is NOT evolving or IN EQUILIBRIUM The Law: p2 + 2pq + q2 = 1 (looks ugly but not impossible)

  44. Conditions of Hardy-Weinberg Law • No mutation • No natural selection • Infinitely large population (no problem with Founder’s effect or genetic drift) • Random mating • No immigration or emigration • If these are met – the gene pool/allele frequency is in equilibrium and NO evolution is in process. • WHAT DO THE ABOVE FACTORS DO FOR THE GENE POOL/ALLELE FREQUENCY? (WRITE/PAIR/SHARE)

  45. Can we use this to look at a populations allele frequency and see if the population is evolving or in equilibrium? Yes

  46. Using Hardy-Weinberg • Albinism is a rare homozygous recessive (aa) trait. • The most characteristic symptom is a deficiency in the skin and hair pigment melanin. • Albinism occurs among humans as well as among other animals. • The average human frequency of albinism in North America is about 1 in 20,000. albino gorilla “Snowflake”

  47. Using Hardy-Weinberg Hardy-Weinberg equation: p2 + 2pq + q2 = 1 q2 = frequency of homozygous recessive individuals (aa) • 1 in 20,000 people with albinism are aa q2 = 1/20,000 = 0.00005 q = .007

  48. Using Hardy-Weinberg Knowing (q), it is easy to solve for (p): p = 1 - q p = 1 - .007 p = .993 • So, the frequency of the dominant allele(A) is .99293 or about 99 in 100.

  49. Using Hardy-Weinberg • Plug the frequencies of p and q into the Hardy-Weinberg equation: • p2+ 2pq + q2= 1 • (.993)2 + 2(.993)(.007) + (.007)2 = 1 • .986 + .014 + .00005 = 1 • p2 = predicted frequency of AA = .986 = 98.6% • 2pq =predicted frequency of Aa = .014 = 1.4% • q2 = predicted frequency of aa = .00005 = .005%

  50. Using Hardy-Weinberg • With a frequency of .005% (about 1 in 20,000), persons with albinism are rare.  • Heterozygous carriers for this trait, with a predicted frequency of 1.4% (about 1in 72), are far more common.  • The majority of humans (98.6%)probably are homozygous dominantand do not have the albinism allele.

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