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Evolution as Genetic Change

Evolution as Genetic Change. 16.2 Evolution as Genetic Change. Natural selection can affect phenotypes in a population in 3 ways Directional Selection Stabilizing Selection Disruptive Selection. Higher fitness at ONE END of curve than at the other

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Evolution as Genetic Change

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  1. Evolution as Genetic Change

  2. 16.2 Evolution as Genetic Change Natural selection can affect phenotypes in a population in 3 ways • Directional Selection • Stabilizing Selection • Disruptive Selection

  3. Higher fitness at ONE END of curve than at the other All phenotypes in population shift toward HIGHER FITNESS Directional Selection # of Individuals in the population Traits of Population

  4. DIRECTIONAL SELECTION Selection Pressure (Against Phenotype) Low Fitness High Fitness New graph shifts in the DIRECTION of Higher Fitness

  5. Directional SelectionExample: Darwin’s Finches # Birds in Population # Birds in Population Beak Size  Beak Size  Small seeds become scarce. Only large seeds are available. Birds with LONGER beaks gather food, survive and reproduce Average Beak Size INCREASES

  6. Higher fitness at the CENTER of the curve Middle Stays THE SAME Ends get NARROWER Stabilizing Selection # of Individuals in the population • EXAMPLE- birth weight of human babies • Smaller than average babies = less likely to be healthy • Larger than average babies = less likely to be healthy Traits of Population

  7. STABILIZING SELECTION Selection Pressure (Against Phenotype) Low Fitness High Fitness Low Fitness New graph is STABILIZEDin the middle

  8. Stabilizing SelectionExample: Human Birth Weight # Babies in Population # Babies in Population Birth Weight Birth Weight Smaller babies are LESS healthy. Larger babies are LESS healthy. Average Sized Babies become Most Common

  9. Higher fitness at TWO ENDS of the curve Middle phenotype DECREASES in frequency Disruptive Selection • EXAMPLE- large seeds and small seeds become more • common and there are few medium seeds • Both birds with small beaks and large beaks are best adapted to eat those seeds • Can result in 2 subgroups # of Individuals in the population Traits of Population

  10. DISRUPTIVE SELECTION Selection Pressure (Against Phenotype) High Fitness Low Fitness High Fitness New graph is DISRUPTED in the middle.

  11. Disruptive SelectionExample: Darwin’s Finches Middle-sized seeds disappear. Only very large and very small seeds are left. # Birds in Population # Birds in Population Beak Size  Beak Size  Average-sized beaks are least common. Birds with VERY LARGE beaks and VERY SMALL beaks are best adapted. This can result in 2 subgroups.

  12. Types Of Selection With Bird Beaks http://player.discoveryeducation.com/index.cfm?guidAssetId=7016E4B0-0335-42A9-BF3E-BB21D2A4D9C8

  13. Which Type of Selection Is It?

  14. RANDOM change in allele frequency Happens by CHANCEEVENTS Happens in SMALLPOPULATIONS NOT NATURALSELECTION (Not related to fitness) Coin Flip 1,000 times How many Heads? 10 times How many Heads? Genetic Drift

  15. A large percentage of a population ISKILLEDor prevented from REPRODUCING INCREASESgenetic drift Bottleneck Effect

  16. Bottleneck EffectsNorthern Elephant Seals Bottleneck Event = HUMANHUNTING(1890s) Population decreased to 20 Seals Now…have have30,000seals With Reduced VARIATION from Bottleneck

  17. The Founder Effect

  18. The Founder Effect Let’s get out of here! • Example: The Cocklebur • Main population with LOTS OF VARIATION (many different colors) • A FEW hitch a ride to an area where there are no cockleburs. • …and start a NEW POPULATION

  19. The Founder Effect We made it! Woo! Now let’s get reproducing! I miss yellow… • They are the FOUNDERS. Their VARIATION gives rise to the variationin the entire NEW POPULATION

  20. Founder Effect A type of Genetic Drift after a SUBGROUP breaks away to form a new population • From Your Articles: Amish Communities in Pennsylvania • Ellis-van Creveld syndrome • EXTRAfingers + toes • Abnormal TEETH + nails • A hole in the HEART

  21. The Founder EffectEllis-von Creveld Syndrome A recessive disorder Founders? SAMUEL KING AND HIS WIFE - 1744

  22. Chance Events and Genetic Drift RANDOMDISASTERS Rock Slide Tsunami Volcano Eruption Meteor Impact Nuclear War Etc.

  23. GENETIC EQUILIBRIUM DEFINITION: Hardy-Weinberg Principle When allele frequencies in a population DON’T CHANGE NO EVOLUTION HAPPENS States that allele frequencies in a population will remain CONSTANT as long as 5 things are true…

  24. Hardy-Weinberg Principle States that allele frequencies in a population will remain constant as long as 5 things are true… • Random Mating • Everyone gets an EQUAL chance to pass on alleles • NO mate selecting

  25. Hardy-Weinberg Principle States that allele frequencies in a population will remain constant as long as 5 things are true… 2. Large Population • Less effect of GENETICDRIFT

  26. Hardy-Weinberg Principle States that allele frequencies in a population will remain constant as long as 5 things are true… 3. No Movement Into or Out of the Population • No MIGRATION • Keep GENEPOOL separate

  27. Hardy-Weinberg Principle States that allele frequencies in a population will remain constant as long as 5 things are true… 4. No Mutations • No NEW alleles in the population

  28. Hardy-Weinberg Principle States that allele frequencies in a population will remain constant as long as 5 things are true… 5. No Natural Selection • All genotypes have equal FITNESS • No ADVANTAGES for anyone

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