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Population Genetics

Population Genetics. Chapter 16 & 17. Vocabulary. Population- a group of individuals living in the same area that breed with each other. . Gene Pool. Gene pool- combination of genetic information from all of the individuals in the population. . What is Genetic Variation?.

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Population Genetics

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  1. Population Genetics Chapter 16 & 17

  2. Vocabulary • Population- a group of individuals living in the same area that breed with each other.

  3. Gene Pool • Gene pool- combination of genetic information from all of the individuals in the population.

  4. What is Genetic Variation? • Differences in alleles of genes • Provides the raw material for natural selection Genetic variation occurs among populations

  5. Sources of Genetic Variation • Mutations- • Changes in the DNA of the individual • If the mutation effects the individuals fitness it will effect the gene pool of the population • Gene Shuffling- • Occurs during the production of gametes • Each chromosome moves independently during meiosis • Crossing over

  6. Relative Frequency • The number of times that an allele occurs in the gene pool. • Relative frequency has nothing to do with dominant and recessive • Evolution involves changes in populations over time 30 20

  7. What is Evolution • How is Evolution measured? • Any change over time in the relative frequencies of alleles in a population • It is populations not individual organisms that can evolve over time

  8. Allele frequencies/ Gene pool Change in relative frequency= evolution

  9. Single Gene vs. Polygenic Traits • The number of phenotypes produced is based on the number of genes that control the trait Controlled by 1 gene produces 2 phenotypes • Traits that are controlled by 2 or more genes • more than 2 alleles for each trait

  10. Natural Selection on Single-gene traits • Individuals either live or die based on their phenotype • A normally brown population of lizards experiences mutations that produce red and black lizards • What will happen to the population? • What if the red lizards stand out more? • What if the black lizards have an advantage over all other lizards?

  11. Natural Selection on Single-gene traits What do you expect the lizard population will look like by generation 50? Explain

  12. Natural Selection on polygenic traits • When fitness varies natural selection can act Three different ways that natural selection can affect the distribution of phenotypes • Directional Selection • Stabilizing Selection • Disruptive Selection

  13. Directional Selection • What would cause this shift? • When individuals at one end of the curve have higher fitness • The range of phenotypes shifts as individuals fail to survive/reproduce

  14. Stabilizing Selection • What causes the shift? • When individuals near the center of the curve have higher fitness then either end

  15. Disruptive Selection • What would cause the shift? • When individuals at either end of the curve have higher fitness then individuals near the middle • Natural selection works hardest on the intermediate type

  16. Genetic Drift • Genetic Drift the random change in allele frequencies based on chance • Some individuals reproduce more times then others • Leave behind more offspring • Has nothing to do with natural selection

  17. Genetic Drift • Relative frequencies move towards those that reproduce more times in the population • Eventually all the individuals in the population will have the same traits

  18. Genetic Drift • Genetic Drift is most common in small populations • In large populations there is a higher chance that individuals will find a mate • Genetic Drift leads to change in relative frequency and therefor evolution

  19. Speciation Diversity of Life

  20. Speciation • Formation of new species • Species: organisms that breed with one another and produce fertile offspring (share the same gene pool) • Caused by natural selection and chance events Donkey Horse Mule

  21. How does speciation happen Shared gene pool Genetic Change in 1 individual Change spreads through the population through reproduction Division/Isolation amongst the population Population begins evolving independently

  22. Reproductive Isolation • Division amongst the population • Population must become reproductively isolated for 2 new species to develop • Allows for mutations/ changes in the gene pool to happen independently 3 types of isolation mechanisms • Behavioral Isolation • Geographic Isolation • Temporal Isolation

  23. Behavioral Isolation • Different behaviors stop the individuals from being attracted to one another • Different mating rituals • Song • Dance • Color pattern • Antler size

  24. Geographic Isolation • Population becomes separated by a geographic barrier • River • Mountain • Bodies of water • Forests • The individuals cannot pass onto the other side of the barrier and therefore cannot mate

  25. Founder Effect • A small group from a population branches off and forms a NEW population • Geographically isolated from the origninal • Individuals carry alleles in different relative frequencies then the original population

  26. Human Influence on Geographic isolation • Man made structures create geographic isolation • Roads • Towns • River Dams

  27. Temporal Isolation • Reproductions times differ • Organisms reproduce at specific times of the day or year • Plants (morning vs. night) • Animals (spring vs. summer vs. fall vs. winter)

  28. Patterns of Evolution 17-4

  29. Microevolution • Small changes in a species that build over time • Accounts for closely related species

  30. Macroevolution • Large-scale evolutionary patterns and process that occur over long periods of time Supports the idea of Common Decent

  31. Punctuated Equilibrium • Patterns of long, stable periods interrupted by brief periods of more rapid change • 100,0001,000,000 years • Changes come in spurts • Caused by • Geographic isolation • Migration • Mass extinctions

  32. Gradualism • Small variations that are hard to notice over a short period of time • Variation takes place slowly (gradually)

  33. Gradualism vs.Punctuated Equilibrium

  34. Extinction • The end of a species or group of species • Natural selection causes extinction • Most common cause for extinction: • Species compete for limited resources • Environments change individuals can’t survive • Why is extinction necessary for evolution to continue? • video

  35. Mass extinction • Mass extinction: many types of living things became extinct at the same time • A the end of the Paleozoic era many organisms died out • 95% of the complex life in the oceans disappeared • Not all organisms disappeared • Reason for mass extinction • Collapsing environment • Caused by multiple factors

  36. How did the extinction of the dinosaurs allow for the diversification of mammals?

  37. Adaptive Radiation • A single species evolves into diverse forms that live in different ways

  38. Convergent Evolution • Process in which unrelated organisms come to resemble each other (Analogous Structures) • “side effect” of adaptive radiation • Takes place among different species that live in similar ecological environments • Face similar environmental demands

  39. Coevolution • The process where 2 species evolve in response to changes in each other • Evolutionary change in one organism induces change in the other • Flowers/pollinator • Predator/Prey

  40. Genetic Equilibrium Hardy-Weinberg Principle

  41. Population Genetics • Evolution is the change in frequencies of alleles in the gene pool of a population • The gene pool has been shifted toward the “b” allele

  42. Genetic Equilibrium • Genetic Equilibrium • The situation in which allele frequencies stay the same with each new generation How likely is it that the allele frequencies will stay the same from one generation to the next?

  43. Hardy-Weinberg principle • Allele frequencies in a population will stay constant unless one or more of the factors are violated • What are some conditions under which NO evolution will occur?

  44. Maintaining equilibrium Genetic Equilibrium: • Random mating • Large population • No movement into or out • No mutations • No natural selection Each of these things can cause evolution to take place!

  45. Random Mating • All individuals must have an equal opportunity to reproduce In nature is mating completely random? Why or why not?

  46. Large populations • Large populations decrease the chances of genetic drift taking place • Why is genetic drift not as common in large populations?

  47. No movement into or out • When individuals move into a population or out of it, the gene pool will change

  48. No mutations What role do mutations play in evolution? • Mutations introduce new alleles into the population

  49. No natural selection • Natural selection gives one phenotype the advantage over the other

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