Chapter 15—The Theory of Evolution

1. Chapter 15—The Theory of Evolution Section 2: Mechanisms of Evolution, Pt. 2

2. 15.2 Continued… • Section Objectives… - Relate changes in genetic equilibrium to mechanisms of speciation. - Explain the role of natural selection in convergent and divergent evolution.

3. Section 15.2 Summary– pages 404-413 The Evolution of Species • The evolution of new species is called ______________ • New species only arise when members of similar populations no longer __________________, meaning they can’t _______________ together speciation interbreed reproduce

4. Three factors may prevent organisms from interbreeding… • ________________ barriers • ________________ barriers • Changes in _________________ number Physical Reproductive chromosome

5. Section 15.2 Summary– pages 404-413 Physical Barriers • In nature, physical barriers can break large populations into _____________ ones. smaller • This process is called ________________ __________________ • What are some examples of geographical/physical barriers? geographic isolation Mountains, oceans, rivers, roads

6. Section 15.2 Summary– pages 404-413 • Tree frogs may exist in a • __________ population. single

7. Section 15.2 Summary– pages 404-413 • ______________ of the rain forest and the formation of a new _________ may _________ the frogs into ______ populations. Destruction river divide two

8. Section 15.2 Summary– pages 404-413 • What color variations exist in the frog populations? • Why might tan frogs survive better on the far side of the river? green and tan There is less greenery so they are camouflaged with the ground

9. Section 15.2 Summary– pages 404-413 • Over time, the divided populations may become two ________ that may no longer __________, even if reunited. species interbreed

10. Section 15.2 Summary– pages 404-413 Reproductive Isolation • Occurs when formerly interbreeding organisms can no longer ___________ and produce _________ offspring… • - This may be due to _______________ or • ________________ reproduce fertile genetics behavior

11. Reproductive Isolation • Genetic Example • A horse and a donkey can mate, but their DNA and genes are too __________________ to produce a fertile offspring? • What is their sterile offspring called? • Since their offspring is sterile, horses and donkeys are considered ___________________ species different mule separate

12. Reproductive Isolation • Behavior Example • One frog species may mate in the ____________, while a different species mates in the __________ • Because of this difference in mating ________________, the two species are reproductively ___________________ spring summer behavior isolated

13. Section 15.2 Summary– pages 404-413 A Change in Chromosome Number • Diploid cells contain ______ sets of chromosomes….one from each ____________ • - Written as ______ • Review… • What are you called if you inherit an extra set of • chromosomes? • - May be written as _____, _____, or so on… two parent 2n polyploid 3n 4n

14. Section 15.2 Summary– pages 404-413 • Polyploidy is possible because sometimes chromosomes fail to separate during meiosis…this is called a _________________ nondisjunction

15. Section 15.2 Summary– pages 404-413 • Remember, meiosis is supposed to create ____________ gametes, but after a nondisjunction they may remain _____________ haploid diploid

16. Section 15.2 Summary– pages 404-413 • What kind of polyploid is formed by the fusion of two 2n gametes? 4n

17. Section 15.2 Summary– pages 404-413 • When a polyploid mates with an individual of the ____________ species, the resulting zygotes may not develop _____________ because of the difference in chromosome numbers…they may also grow up to be ______________ normal normally infertile • However, polyploids can interbreed with ________________, forming a separate species each other

18. Section 15.2 Summary– pages 404-413 Speciation rates • Scientists argue that species may evolve at different ___________ • Two theories exist covering speciation rates • _______________________ • ________________________ rates gradualism punctuated equilibrium

19. Section 15.2 Summary– pages 404-413 Gradualism • The idea that species originate through a __________, gradual change of inherited adaptations. slow • Some evidence from the ________ record supports gradualism. fossil

20. Punctuated Equilibrium • Proposed in 1972 by Niles ______________ and Stephen J. _____________ Eldridge Gould • This hypothesis argues that speciation occurs relatively quickly, in _______ bursts, with long periods of genetic equilibrium in between. • may occur after major ______________ • changes or mass ________________ rapid climatic extinctions

21. Section 15.2 Summary– pages 404-413 Patterns of Evolution • Biologists have observed two different _______________ of evolution that occur throughout the world in different natural environments. • _____________________ evolution • _____________________ evolution patterns Divergent Convergent

22. Divergent Evolution • What does diverge mean? • So this pattern of evolution occurs when a ___________ ancestor diverges into ______________ species • Usually occurs when populations change as they adapt to new __________________ to move apart common separate environments

23. Divergent Evolution—Adaptive Radiation • A special type of divergent evolution is called ____________________ ____________________ • It occurs when an ancestral species evolves into an ____________ of species to fit a number of diverse _______________ and ____________ • Common on ________________ adaptive radiation array habitats niches islands

24. Why might these birds on the Hawaiian Islands have so many different types of beaks? due to different food sources

25. Convergent Evolution • What does converge mean? • So this pattern of evolution occurs when _______________ species develop similarities because they live in similar _______________ to come together different environments

26. Similar to how a dolphin and shark converged • What habitat do they share? • What structures do they share? The ocean fins, body shape Marine mammal Shark—Type of Fish

27. Objective 2 • Relate changes in genetic equilibrium to mechanisms of speciation. Geographic isolation Reproductive isolation – genetic or behavior Changes in chromosome #

28. Objective 3 • Explain the role of natural selection in convergent and divergent evolution. Similar species inherit different traits because they are in different environments Different species inherit similar traits because they are in similar environments