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Chapter 17: Population Genetics and Speciation

Chapter 17: Population Genetics and Speciation. Section 1: Genetic Variation. 1. One can study evolution in two scales, microevolution and macroevolution 2. Population genetics is the study of the frequency and interaction of alleles and genes in populations

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Chapter 17: Population Genetics and Speciation

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  1. Chapter 17: Population Genetics and Speciation

  2. Section 1: Genetic Variation • 1. One can study evolution in two scales, microevolution and macroevolution • 2. Population geneticsis the study of the frequency and interaction of alleles and genes in populations • 3. Before anyone understood genetics, the only kind of variation that could be observed and measured was phenotypic variation.

  3. 4. We know inherited units as alleles. • 5. A distribution is an overview of the relative frequency and range of a set of values. • A normal distribution simply means a tendency to cluster around an average value

  4. 7. A gene pool is the particular combination of alleles in a population at any one point in time • 8. Genetic variation is measured in terms of the frequency of alleles in the gene pool of a population • 9. Frequency is a proportion or ratio of a group that is of one type • 10. Evolution cannot proceed if there is no variation.

  5. 11. The major source of new alleles in natural populations is mutation in germ cells. • What are germ cells? • Gametes • 12. Are mutations in somatic cells passed on to offspring? • NO!

  6. Section 2: Genetic Change • 13. The forces that act on a population and can cause evolution are: • Gene Flow • Nonrandom Mating • Genetic Drift • Mutation • Natural Selection

  7. 14. Gene flow can by caused by migration, the movement of individuals from one population to another. • 15. Non-random mating occurs in populations because of sexual selection and inbreeding • 16. Genetic drift can cause rare alleles to be lost from one generation to the next.

  8. 17.

  9. 18. The process of natural selection is a result of: • All populations have genetic variation. • Individuals tend to produce more offspring than the environment can support. • All populations depend upon the reproduction of individuals. • 19. “Evolutionary fitness is measured in grandchildren” means that an individual must survive to reproduce, and also produce offspring that can reproduce, to pass its genes on to future generations

  10. 20. The result of natural selection is that the frequency of an allele may increase or decrease depending on the allele’s effects on survival and reproduction. • 21. In natural selection, environment (nature) does the selection. • 22. Natural selection does not create perfectly adapted organisms. • 23. The effects of natural selection can often be seen in behaviors such as ?

  11. Directional Selection • One of the extreme variations is favored • Result: rapid evolution • Ex. After drought, hard seeds are left to birds that have tougher beaks that can crack open the seeds • Ex. In book: antibiotic resistant bacteria http://www.detectingdesign.com/images/NaturalSelection/natura2.jpg

  12. Stabilizing selection • Average (intermediate) individuals are favored • Result: variation is reduced in a population • Ex. Small spiders have a harder time of finding food; large spiders are easily targeted by predators http://www.kmitl.ac.th/agritech/nutthakorn/04090035_2202/multiweb/environ/images/be_13.gif

  13. Disruptive Selection • Individuals with either extreme are favored • Results: evolution of two species (speciation) • Ex. Dark and light colored limpets

  14. http://abyss.uoregon.edu/~js/images/selection_change.gif

  15. Section 3: Speciation • 24. Species are not permanent things. • 25. A species is a group of natural populations that can interbreed and produce healthy, fertile offspring • 26. Divergence is the accumulation of differences between populations and can lead to the formation of new species • 27. Speciation is the process of forming new species by evolution from preexisting species

  16. 28. Reproductive isolation is a state in which two populations can no longer interbreed to produce future offspring.

  17. 29. Geographic isolation is when a physical barrier arises between populations to prevent interbreeding.

  18. 30. If two populations develop differences in specific behaviors for mating or timing of mating, they may no longer attract each other for mating.

  19. 31. Many cases of extinction are the result of environmental change • It is estimated that more than 99% of all species that have ever lived are extinct

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