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Overview

Overview. Evolution Section 16-2. Genetic Drift. Genetic Drift– can cause allele frequencies to change based on chance Based on these two examples Founder effect Bottleneck effect. Types of Natural Selection. Directional selection Example of Darwin’s Beak Size Disruptive selection

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Overview

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  1. Overview Evolution Section16-2

  2. Genetic Drift • Genetic Drift– can cause allele frequencies to change based on chance • Based on these two examples • Founder effect • Bottleneck effect

  3. Types of Natural Selection • Directional selection • Example of Darwin’s Beak Size • Disruptive selection • Acts against the intermediate type and favors two Distinct subpopulations • Stabilizing selection • Keeps phenotypes stable for long periods of time. Example (Babies birth’s weights • Are 6 to 8 pounds

  4. Chapter 16-3and Ch 17-4 Evolution Mechanisms The Process of Speciation

  5. Speciation: Formation of New Species Reproductive isolation must be achieved!

  6. Reproductive Isolation • 4a This occurs when the members of two populations cannot interbreed and thus become reproductively isolated -causing separation of Gene Pools • 4b. And Ultimately new species arrive.

  7. Behavioral Isolation • Occurs when two populations are capable of inter-breeding but choose not-to because of different courtship rituals or other reproductive strategies.

  8. Isolation in Cheetahs Behavioral isolation is important because it prevents one species from breeding with another species. Observations of complete courting behavior and mating of cheetahs in the wild are very rare.

  9. First, their basic courting behavior is similar to other cats. • Second, we know that breeding behavior within a species is often highly ritualized and there are distinct differences between closely related species.

  10. Cheetah Example • If a particular breeding sequence is altered in anyway, • breeding does not occur. • We can only assume that there are enough differences in breeding behavior of the cheetah so that it cannot breed with the lions and leopards that are found in the same

  11. Geographic Isolation • This occurs when two populations are seperated by geographic barriers such as a river or a canyon or large bodies of water.

  12. Temporal Isolation Example: When two or more species reproduce at two different times or seasons.

  13. Types of Speciation • Allopatric Speciation • Geographic isolation – • Adaptive Radiation- A process by which a single species or a group of species evolve into several different forms that live in different ways. (Fossil Record as Evidence)

  14. Convergent Evolution • A process of evolution when unrelated organisms come to resemble one another. • Evidence: Homologous Structures- Flippers of Dolphins have similar Wings of Penguins.

  15. Convergent Evolution

  16. Sympatric Speciation • Almost always in plants • In same population but do not interbreed • Coevolution: The Process by which two species evolve in response to changes in each other over time.

  17. Rates of Evolution Gradualism vs. Punctuated Equilibrium

  18. Punctuated Equillibrium • a theory in evolutionary biology. It states that most sexually reproducing populations will show little change for most of their geological history, and that when phenotypic evolution does occur.

  19. Gradualism Theory • phyletic gradualism, which states that evolution generally occurs uniformly and by the steady and gradual transformation • In this view, evolution is seen as generally smooth and continuous.

  20. The Two Competing Theories

  21. #16 • Giraffes and zebras both came from a common ancestor, • But the theorists describe it as different patterns in evolution

  22. Questions for Video to answer • #1What do the Rough Skinned Newts do to protect themselves from the predators? • #2. What has happened to the poison levels’ in the toxic newt’s response to the snake?

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