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KEY CONCEPT  Natural selection is not the only mechanism through which populations evolve.
<ul><li>Gene flow is the movement of alleles between populations.  </li></ul><ul><li>Gene flow occurs when individuals joi...
<ul><li>Genetic drift is a change in allele frequencies due to chance.  </li></ul><ul><li>Genetic drift causes a loss of g...
<ul><li>The founding of a small population can lead to genetic drift. </li></ul><ul><ul><li>It occurs when a few individua...
<ul><li>Genetic drift has negative effects on a population.  Why? </li></ul><ul><ul><li>Some important alleles that help i...
<ul><li>Sexual selection occurs when certain traits increase mating success.  </li></ul><ul><li>Sexual selection occurs du...
<ul><li>There are two types of sexual selection. </li></ul><ul><ul><li>intrasexual selection: competition among males </li...
KEY CONCEPT  Hardy-Weinberg equilibrium provides a framework for understanding how populations evolve.
<ul><li>Hardy-Weinberg equilibrium describes populations that are not evolving.  </li></ul><ul><li>Biologists use models t...
<ul><li>Hardy-Weinberg equilibrium describes populations that are not evolving.  </li></ul><ul><li>Genotype frequencies st...
<ul><li>Hardy-Weinberg equilibrium describes populations that are not evolving.  </li></ul><ul><li>Real populations rarely...
<ul><li>The Hardy-Weinberg equation is used to predict genotype frequencies in a population.  </li></ul><ul><li>Predicted ...
<ul><li>There are five factors that can lead to evolution.  </li></ul>
<ul><li>Genetic drift changes allele frequencies due to chance alone.  How can this lead to evolution? </li></ul>
<ul><li>Gene flow moves alleles from one population to another. How can this lead to evolution? </li></ul>
<ul><li>Mutations produce the genetic variation needed for evolution.  How can this lead to evolution? </li></ul>
<ul><li>Sexual selection selects for traits that improve mating success. How can this lead to evolution? </li></ul>
<ul><li>Natural selection selects for traits advantageous for survival. How can this lead to evolution? </li></ul>
<ul><li>In nature, populations evolve. </li></ul><ul><ul><li>expected in all populations most of the time </li></ul></ul><...
KEY CONCEPT  New species can arise when populations are isolated.
<ul><li>The isolation of populations can lead to speciation.  </li></ul><ul><li>Populations become isolated when there is ...
<ul><li>Reproductive isolation can occur between isolated populations. </li></ul><ul><ul><li>members of different populati...
<ul><li>Populations can become isolated in several ways.  Give one example. </li></ul><ul><li>Behavioral barriers can caus...
<ul><li>Geographic barriers can cause isolation. </li></ul><ul><ul><li>called geographic isolation </li></ul></ul><ul><ul>...
<ul><li>How will a showy trait in males become established in a population?  </li></ul><ul><li>A.  Males with a showy trai...
<ul><li>How will a showy trait in males become established in a population?  </li></ul><ul><li>A.  Males with a showy trai...
<ul><li>How are the bottleneck effect and founder effect similar?  </li></ul><ul><li>A.  Both add genetic variation to the...
<ul><li>How are the bottleneck effect and founder effect similar?  </li></ul><ul><li>A.  Both add genetic variation to the...
<ul><li>How might gene flow benefit a small population?  </li></ul><ul><li>A.  Harmful alleles could leave the population....
<ul><li>How might gene flow benefit a small population?  </li></ul><ul><li>A.  Harmful alleles could leave the population....
Review <ul><li>Gene flow is the mixing of genes among populations </li></ul><ul><li>Low gene flow increases the chances of...
Review <ul><li>Hardy-Weinberg Evolution – a model to explain a population that is not evolving – used to predict gene freq...
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Unit 12 Mechanisms For Evolution

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Transcript of "Unit 12 Mechanisms For Evolution"

  1. 1. KEY CONCEPT Natural selection is not the only mechanism through which populations evolve.
  2. 2. <ul><li>Gene flow is the movement of alleles between populations. </li></ul><ul><li>Gene flow occurs when individuals join new populations and reproduce. </li></ul><ul><li>Gene flow keeps neighboring populations similar. </li></ul><ul><li>Low gene flow increases the chance that two populations will evolve into different species. </li></ul><ul><li>How? </li></ul>bald eagle migration
  3. 3. <ul><li>Genetic drift is a change in allele frequencies due to chance. </li></ul><ul><li>Genetic drift causes a loss of genetic diversity. </li></ul><ul><li>It is most common in small populations. </li></ul><ul><li>A population bottleneck can lead to genetic drift. </li></ul><ul><ul><li>It occurs when an event drastically reduces population size. </li></ul></ul><ul><ul><li>The bottleneck effect is genetic drift that occurs after a bottleneck event. </li></ul></ul><ul><ul><li>How will the resulting </li></ul></ul><ul><ul><li>population be different? </li></ul></ul>
  4. 4. <ul><li>The founding of a small population can lead to genetic drift. </li></ul><ul><ul><li>It occurs when a few individuals start a new population. </li></ul></ul><ul><ul><li>The founder effect is genetic drift that occurs after start of new population. How will the new population be different? </li></ul></ul>
  5. 5. <ul><li>Genetic drift has negative effects on a population. Why? </li></ul><ul><ul><li>Some important alleles that help in survival disappear from the population </li></ul></ul><ul><ul><li>less likely to have some individuals that can adapt </li></ul></ul><ul><ul><li>harmful alleles can become more common due to chance </li></ul></ul>
  6. 6. <ul><li>Sexual selection occurs when certain traits increase mating success. </li></ul><ul><li>Sexual selection occurs due to higher cost of reproduction for females. </li></ul><ul><ul><li>males produce many sperm continuously </li></ul></ul><ul><ul><li>females are more limited in potential offspring each cycle </li></ul></ul><ul><li>Name some species that use sexual selection when mating. </li></ul>
  7. 7. <ul><li>There are two types of sexual selection. </li></ul><ul><ul><li>intrasexual selection: competition among males </li></ul></ul><ul><ul><li>intersexual selection: males display certain traits to females </li></ul></ul>
  8. 8. KEY CONCEPT Hardy-Weinberg equilibrium provides a framework for understanding how populations evolve.
  9. 9. <ul><li>Hardy-Weinberg equilibrium describes populations that are not evolving. </li></ul><ul><li>Biologists use models to study populations. Why? </li></ul><ul><li>Hardy-Weinberg equilibrium is a type of model. </li></ul>
  10. 10. <ul><li>Hardy-Weinberg equilibrium describes populations that are not evolving. </li></ul><ul><li>Genotype frequencies stay the same if five conditions are met. </li></ul><ul><ul><li>very large population: no genetic drift </li></ul></ul><ul><ul><li>no emigration or immigration: no gene flow </li></ul></ul><ul><ul><li>no mutations: no new alleles added to gene pool </li></ul></ul><ul><ul><li>random mating: no sexual selection </li></ul></ul><ul><ul><li>no natural selection: all traits aid equally in survival </li></ul></ul>
  11. 11. <ul><li>Hardy-Weinberg equilibrium describes populations that are not evolving. </li></ul><ul><li>Real populations rarely meet all five conditions. </li></ul><ul><ul><li>Real population data is compared to a model. </li></ul></ul><ul><ul><li>Models are used to studying how populations evolve. </li></ul></ul>
  12. 12. <ul><li>The Hardy-Weinberg equation is used to predict genotype frequencies in a population. </li></ul><ul><li>Predicted genotype frequencies are compared with actual frequencies. </li></ul><ul><ul><li>used for traits in simple dominant-recessive systems </li></ul></ul><ul><ul><li>must know frequency of recessive homozygotes </li></ul></ul><ul><li>p 2 + 2pq + q 2 = 1 </li></ul>&quot;The Hardy-Weinberg equation is based on Mendelian genetics. It is derived from a simple Punnett square in which p is the frequency of the dominant allele and q is the frequency of the recessive allele.&quot;
  13. 13. <ul><li>There are five factors that can lead to evolution. </li></ul>
  14. 14. <ul><li>Genetic drift changes allele frequencies due to chance alone. How can this lead to evolution? </li></ul>
  15. 15. <ul><li>Gene flow moves alleles from one population to another. How can this lead to evolution? </li></ul>
  16. 16. <ul><li>Mutations produce the genetic variation needed for evolution. How can this lead to evolution? </li></ul>
  17. 17. <ul><li>Sexual selection selects for traits that improve mating success. How can this lead to evolution? </li></ul>
  18. 18. <ul><li>Natural selection selects for traits advantageous for survival. How can this lead to evolution? </li></ul>
  19. 19. <ul><li>In nature, populations evolve. </li></ul><ul><ul><li>expected in all populations most of the time </li></ul></ul><ul><ul><li>respond to changing environments </li></ul></ul>
  20. 20. KEY CONCEPT New species can arise when populations are isolated.
  21. 21. <ul><li>The isolation of populations can lead to speciation. </li></ul><ul><li>Populations become isolated when there is no gene flow. </li></ul><ul><ul><li>Isolated populations adapt to their own environments. </li></ul></ul><ul><ul><li>Genetic differences can add up over generations. </li></ul></ul><ul><ul><li>How could this lead to a new species? </li></ul></ul>
  22. 22. <ul><li>Reproductive isolation can occur between isolated populations. </li></ul><ul><ul><li>members of different populations cannot mate successfully </li></ul></ul><ul><ul><li>final step to becoming separate species </li></ul></ul><ul><li>Speciation is the rise of two or more species from one existing species. </li></ul>
  23. 23. <ul><li>Populations can become isolated in several ways. Give one example. </li></ul><ul><li>Behavioral barriers can cause isolation. </li></ul><ul><ul><li>called behavioral isolation </li></ul></ul><ul><ul><li>includes differences in courtship or mating behaviors </li></ul></ul>
  24. 24. <ul><li>Geographic barriers can cause isolation. </li></ul><ul><ul><li>called geographic isolation </li></ul></ul><ul><ul><li>physical barriers divide population – what could happen to cause a new barrier to form? </li></ul></ul><ul><li>Temporal barriers can cause isolation. </li></ul><ul><ul><li>called temporal isolation </li></ul></ul><ul><ul><li>timing of reproductive periods prevents mating </li></ul></ul>
  25. 25. <ul><li>How will a showy trait in males become established in a population? </li></ul><ul><li>A. Males with a showy trait will mate more often and be more likely to pass the allele for the trait to offspring. </li></ul><ul><li>B. Males with a showy trait are more likely to survive. </li></ul><ul><li>C. Showy traits are dominant, so they become established in the gene pool. </li></ul><ul><li>D. Alleles for showy traits are not lost due to genetic drift. </li></ul>
  26. 26. <ul><li>How will a showy trait in males become established in a population? </li></ul><ul><li>A. Males with a showy trait will mate more often and be more likely to pass the allele for the trait to offspring. </li></ul><ul><li>B. Males with a showy trait are more likely to survive. </li></ul><ul><li>C. Showy traits are dominant, so they become established in the gene pool. </li></ul><ul><li>D. Alleles for showy traits are not lost due to genetic drift. </li></ul><ul><li>Correct Answer = A </li></ul>
  27. 27. <ul><li>How are the bottleneck effect and founder effect similar? </li></ul><ul><li>A. Both add genetic variation to their gene pools. </li></ul><ul><li>B. Both result in loss of certain alleles from their gene pools. </li></ul><ul><li>C. Both result in their gene pools becoming larger. </li></ul><ul><li>D. In both, a small population with a varied gene pool forms from a large population with little variation. </li></ul>
  28. 28. <ul><li>How are the bottleneck effect and founder effect similar? </li></ul><ul><li>A. Both add genetic variation to their gene pools. </li></ul><ul><li>B. Both result in loss of certain alleles from their gene pools. </li></ul><ul><li>C. Both result in their gene pools becoming larger. </li></ul><ul><li>D. In both, a small population with a varied gene pool forms from a large population with little variation. </li></ul><ul><li>Correct Answer = B </li></ul>
  29. 29. <ul><li>How might gene flow benefit a small population? </li></ul><ul><li>A. Harmful alleles could leave the population. </li></ul><ul><li>B. The population might evolve into two species. </li></ul><ul><li>C. The flow of alleles into a population can decrease variation. </li></ul><ul><li>D. The flow of alleles into a population can increase variation. </li></ul>
  30. 30. <ul><li>How might gene flow benefit a small population? </li></ul><ul><li>A. Harmful alleles could leave the population. </li></ul><ul><li>B. The population might evolve into two species. </li></ul><ul><li>C. The flow of alleles into a population can decrease variation. </li></ul><ul><li>D. The flow of alleles into a population can increase variation. </li></ul><ul><li>Correct Answer = D </li></ul>
  31. 31. Review <ul><li>Gene flow is the mixing of genes among populations </li></ul><ul><li>Low gene flow increases the chances of a population becoming two species </li></ul><ul><li>Genetic drift causes a loss of diversity – usually occurs after a significant event lowers the population dramatically – has a negative affect on the population </li></ul><ul><li>The founder effect can cause genetic drift if a small number of individuals found a new area </li></ul><ul><li>Sexual selection occurs when a characteristic increases the chance of mating </li></ul><ul><ul><li>Intrasexual – members of the same sex compete </li></ul></ul><ul><ul><li>Intersexual – members of one sex “show off” for the other </li></ul></ul>
  32. 32. Review <ul><li>Hardy-Weinberg Evolution – a model to explain a population that is not evolving – used to predict gene frequency </li></ul><ul><li>There are five factors that can lead to evolution </li></ul><ul><ul><li>Genetic drift changes allele frequencies due to chance </li></ul></ul><ul><ul><li>Gene flow moves alleles from one population to another </li></ul></ul><ul><ul><li>Mutations produce the genetic variation needed for evolution </li></ul></ul><ul><ul><li>Sexual selection selects for traits advantageous for mating </li></ul></ul><ul><ul><li>Natural selection selects for traits advantageous for survival </li></ul></ul><ul><li>Isolated populations adapt to their environments and genetic differences add up over generations </li></ul><ul><li>Final step to speciation is inability to reproduce </li></ul><ul><li>Behavioral, geographic, and temporal barriers can all result in speciation </li></ul>
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