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Chapter 22

Chapter 22. Descent With Modification. On the Origin of Species by Means of Natural Selection. Darwin’s theory explained what had once been a bewildering array of unrelated observations . The great diversity of organisms Their origins and relationships

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Chapter 22

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  1. Chapter 22 Descent With Modification

  2. On the Origin of Species by Means of Natural Selection • Darwin’s theory explained what had once been a bewildering array of unrelated observations. • The great diversity of organisms • Their origins and relationships • Their similarities and differences • Their geographic distribution • Their adaptations to surrounding environments

  3. Concepts that Influenced Darwin • Linnaeus- system of classification • Lamark and Erasmus Darwin- species can change • Hutton and Lyell- Gradual geologic change • Malthus- Population limits, struggle for survival • Cuvier- The older the fossil, the less it resembles living creatures that exist today, catastrophic events and extinction.

  4. Darwin's Theory of Evolution through Natural Selection 5 observations and 3 inferences Summarize Darwin’s Theory. • OVERPRODUCTION: Species produce more offspring than can survive • DIFFERENTIAL SUCCESS: Not all individuals in a population survive, making populations stable except for seasonal fluctuations. • COMPETITION: Resources are limited so individuals must compete to survive. INFERENCE #1: Overproduction leads to competition for resources and differential survival. • VARIATION: Members of a population vary extensively in their characteristics; no two individuals are exactly alike • TRAITS ARE HERITABLE: Variations in traits are heritable. INFERENCE #2: Individuals whose inherited traits help them survive and obtain resources are more likely to reproduce and pass on their traits to the next generation. INFERENCE #3: Differential success of individuals with advantageous traits will lead to a gradual change in a population; favorable traits will acccumuleover generations.

  5. The way you use the following terms is VERY important • Fitness= reproducing more than others • An adaptation= any trait that helps an organism survive, obtain resources and reproduce more • Individuals DO NOT evolve, POPULATIONS evolve • Individuals do not “become adapted,” they “have adaptations” that make them more fit. • POPULATIONS can become adapted to an environment over successive generations • The fitness of individuals is determined by the environment

  6. Evolution through Natural Selection Explains a wide range of observations Homology: shared features due to common ancestry Natural Selection modifies existing structures • anatomical homology • vestigial structures • anatomical similarities in vertebrate embryos • molecular machinery such as DNA or RNA sequences, or proteins such as the cytoskeleton in all eukaryotes

  7. Anatomical Homology

  8. Vestigial Structures: Homologous structures that are significantly reduced in size and importance for the organism, but remain because they are inherited from the ancestor • Example: Pelvis in Baleen Whale

  9. Homology in Embryonic Development All vertebrates have (at some point in their life) • A notochord- a strong but flexible rod along the back • A dorsal hollow nerve chord • Pharyngeal slits/ pouch • Post anal tail

  10. Molecular homology • Similarities in DNA, RNA, and Protein Sequence are evidence of common ancestry

  11. Natural Selection Explains Convergence • Convergent Evolution: When distantly related organism evolve similar characteristics due to environmental pressure and natural selection

  12. Ch 23 • Population Genetics • Hardy Weinberg Equation

  13. How do we define evolution in modern terms? • Evolution is the change in the genetic composition of a population over generations. • Gene Pool: all the alleles of all the gene loci of all the individuals in a population

  14. The Hardy-Weinberg Theorem • The allele frequencies of a population will remain constant If only Mendelian segregation and independent assortment are at work. • What is the frequency of the CR and CW alleles in each generation?

  15. Conditions of Hardy-Weinberg The Hardy–Weinberg theorem describes a hypothetical population that is NOT EVOLVING. For a population to not evolve it must meet the following five conditions 1. Extremely large population size. 2. No gene flow or transfer of alleles between populations.3. No mutations. 4. Random mating. 5. No natural selection.  Meeting these conditions is practically impossible.

  16. The Hardy-Weinberg Equation • p2 + 2pq + q2 = 1 • p + q = 1 • p = frequency of dominant allele • q = frequency of recessive allele

  17. Example Hardy-Weinberg Calculations • Phenylketonuria (PKU) is an autosomal recessive genetic disease that affects 1/10,000 births. • Calculate the frequency of q (the recessive allele) • Calculate the frequency of p (the dominant allele) • What percentage of the population are carriers of the PKU allele?

  18. The Fossil Record Gives us information about when particular types of organisms arose, what types of structures they had and how abundant they were

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