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Chapter 24

The Origin of Species. Chapter 24. 24.1. The biological species concept emphasizes reproductive isolation. Microevolution. Focuses on the change in genetic frequencies for a trait in a population over time (HWE). What is a species?.

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Chapter 24

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  1. The Origin of Species Chapter 24

  2. 24.1 The biological species concept emphasizes reproductive isolation

  3. Microevolution • Focuses on the change in genetic frequencies for a trait in a population over time (HWE)

  4. What is a species? • Organisms of the same group that can interbreed and produce fertile offspring

  5. Biological Species Concept • A population whose members have the potential to: • Interbreed with one another and • Produce viable, fertile offspring but • Who cannot produce viable, fertile offspring with members of other species

  6. What does this mean? • Reproductive isolation is the key • once similar organisms are no longer able to interbreed in nature, they are considered to be another species • Speciation has occurred

  7. Reproductive Isolation • Barriers that prevent two species from producing viable, fertile hybrids

  8. Pre-zygotic Barriers • Prevent successful mating • No fertilized eggs (zygotes)

  9. Habitat Isolation • Species live in different locations may never meet and thus will never mate

  10. Behavioral Isolation • If mating behaviors are dissimilar among species, mating may not occur • Unique behaviors allow own species recognition • Blue footed booby dance

  11. Temporal Isolation • Breed or flower at different times

  12. Mechanical Isolation • The reproductive organs of two species are incompatible • Galearis diantha and Ponerorchis chusua orchids pollinated by different species of bees

  13. Gametic Isolation • Gametes of 2 species may not meet due to chemical barriers preventing survival of sperm • Important to aquatic species

  14. Post-zygotic Barriers • Barriers that prevent the hybrid zygote from becoming a viable, fertile adult.

  15. Reduced Hybrid Viability • Genetic incompatibility may force miscarriage of hybrid embryo Zygote (blue) forms but soon aborts (clear)

  16. Reduced Hybrid Fertility • Robust, viable offspring produced • Adult hybrid organism is sterile

  17. Hybrid Breakdown • 1st generation hybrids are fertile but subsequent generations are not Rice strains whose offspring are fertile but those offspring are not; accumulation of mutations over generations cause sterility

  18. Limitations to Biological Species Concept • Does not account for asexually reproducing organisms, like bacteria • Does not account for interbreeding that may have happened in fossil species

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