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Origin of Species

Origin of Species. 3/30/09. Fig. 24-3a. Gene flow between populations. Example of a gene tree for population pair A-B. Allele. Population. Gene flow event. 1. B. Allele 1 is more closely related to alleles 2, 3, and 4 than to alleles 5, 6, and 7. Inference: Gene flow occurred. 2. A.

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Origin of Species

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  1. Origin of Species 3/30/09

  2. Fig. 24-3a Gene flow between populations Example of a gene tree for population pair A-B Allele Population Gene flow event 1 B Allele 1 is more closely related to alleles 2, 3, and 4 than to alleles 5, 6, and 7. Inference: Gene flow occurred. 2 A A 3 4 A 5 B Alleles 5, 6, and 7 are more closely related to one another than to alleles in population A. Inference: No gene flow occurred. 6 B B 7

  3. Fig. 24-4a Prezygotic barriers Mechanical Isolation Habitat Isolation Temporal Isolation Behavioral Isolation Individuals of different species Mating attempt (e) (f) (a) (c) (d) (b)

  4. Fig. 24-4i Prezygotic barriers Postzygotic barriers Reduced Hybrid Viability Reduced Hybrid Fertility Hybrid Breakdown Gametic Isolation Viable, fertile offspring Fertilization (h) (g) (l) (i) (j) (k)

  5. Fig. 24-9a EXPERIMENT Initial population Some flies raised on starch medium Some flies raised on maltose medium Mating experiments after 40 generations

  6. Fig. 24-9b RESULTS Female Female Starch Starch Starch Maltose population 1 population 2 population 1 Starch Starch 15 9 18 22 Male Male Maltose 15 8 20 12 population 2 Starch Mating frequencies in experimental group Mating frequencies in control group

  7. Fig. 24-10-1 2n = 6 4n = 12 Failure of cell division after chromosome duplication gives rise to tetraploid tissue.

  8. Fig. 24-10-2 2n 2n = 6 4n = 12 Failure of cell division after chromosome duplication gives rise to tetraploid tissue. Gametes produced are diploid..

  9. Fig. 24-10-3 2n 2n = 6 4n = 12 4n Failure of cell division after chromosome duplication gives rise to tetraploid tissue. Gametes produced are diploid.. Offspring with tetraploid karyotypes may be viable and fertile.

  10. Fig. 24-11-1 Species B 2n = 4 Unreduced gamete with 4 chromosomes Meiotic error Normal gamete n = 3 Species A 2n = 6

  11. Fig. 24-11-2 Species B 2n = 4 Unreduced gamete with 4 chromosomes Hybrid with 7 chromosomes Meiotic error Normal gamete n = 3 Species A 2n = 6

  12. Fig. 24-11-3 Species B 2n = 4 Unreduced gamete with 4 chromosomes Unreduced gamete with 7 chromosomes Hybrid with 7 chromosomes Meiotic error Normal gamete n = 3 Normal gamete n = 3 Species A 2n = 6

  13. Fig. 24-11-4 Species B 2n = 4 Unreduced gamete with 4 chromosomes Unreduced gamete with 7 chromosomes Hybrid with 7 chromosomes Meiotic error Viable fertile hybrid (allopolyploid) 2n = 10 Normal gamete n = 3 Normal gamete n = 3 Species A 2n = 6

  14. Fig. 24-14-1 Gene flow Barrier to gene flow Population (five individuals are shown)

  15. Fig. 24-14-2 Isolated population diverges Gene flow Barrier to gene flow Population (five individuals are shown)

  16. Fig. 24-14-3 Isolated population diverges Hybrid zone Gene flow Hybrid Barrier to gene flow Population (five individuals are shown)

  17. Fig. 24-14-4 Isolated population diverges Possible outcomes: Hybrid zone Reinforcement OR Fusion Gene flow Hybrid OR Barrier to gene flow Population (five individuals are shown) Stability

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