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Chapter 23 & 24 Population Genetics and Speciation

Chapter 23 & 24 Population Genetics and Speciation. Evolution descent with modification genetic change over time Natural Selection differential reproductive success different phenotypes result from interaction of organisms with environment

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Chapter 23 & 24 Population Genetics and Speciation

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  1. Chapter 23 & 24 Population Genetics and Speciation

  2. Evolution • descent with modification • genetic change over time • Natural Selection • differential reproductive success • different phenotypes result from interaction of organisms with environment • Natural selection causes changes in relative frequencies of alleles in a population

  3. Population • Population genetics • Gene pool

  4. Mendel's work provided the underlying explanation for variation in traits • Particulate hypothesis • Microevolution • Populations are the smallest unit of study for evolution

  5. Factors that produce genetic variation • Mutation • Sexual recombination • Crossing over • Independent assortment • Random fertilization

  6. Allele frequencies are directly related to genotype frequencies • To calculate the allele frequencies at a particular loci, you must know: • mode of inheritance • number of alleles involved

  7. Hardy and Weinberg • developed a mathematical model for estimating allele frequencies • single locus, two allele system that demonstrates dominant/recessive inheritance • (p+q) X (p+q) = p2 + 2pq + q2 male female next generation • Hardy-Weinberg equilibrium: p2 + 2pq + q2 = 1

  8. Assumptions of HW: (an ideal population) • large population size • no gene flow between populations • no mutation • no natural selection • random mating

  9. In a non-evolving population: • Allele frequencies will remain constant from one generation to the next • Said to be at Hardy-Weinberg Equilibrium

  10. Factors that influence allele frequencies • Natural selection  • Gene flow 3. Genetic drift • founder effect • bottleneck effect

  11. Natural selection

  12. Genetic drift

  13. Bottleneck effect

  14. Genetic drift is significant in small populations • Genetic drift causes allele frequencies to change at random • Genetic drift can lead to a loss of genetic variation within populations • Genetic drift can cause harmful alleles to become fixed

  15. Adaptive Evolution • chance events produce variation and natural selection favors some forms more than others • fitness

  16. Most species exhibit geographic variation • Differences between gene pools of separate populations • Natural selection contributes to phenomenon

  17. Modes of selection

  18. Sexual selection

  19. What preserves genetic variation? • Diploidy • Heterozygote advantage • Neutral Variation

  20. Why can’t natural selection produce “perfect organisms” 1. historical constraints 2. adaptations are usually compromises 3. role of chance 4. selection can only edit existing variation

  21. Speciation is a focal point of evolution • appearance of new species is source of diversity • originate through divergence of gene pools • Fossil record reveals cumulative effects of speciation over time • macroevolution

  22. Biological species concept • Individuals that have the ability to interbreed and produce fertile offspring

  23. Reproductive isolation • Biological species are distinguished based on reproductive incompatibility • Prezygotic barriers • Postzygotic barriers • Hybrids

  24. Reproductive Barriers Prezygotic barriers Postzygotic barriers Habitat Isolation Behavioral Isolation Temporal Isolation Mechanical Isolation Gametic Isolation Reduced Hybrid Viability Reduced Hybrid Fertility Hybrid Breakdown Individuals of different species Viable, fertile offspring Mating attempt Fertilization (c) (e) (f) (a) (g) (h) (l) (i) (d) (j) (b) (k)

  25. Alternate Species Definitions • Paleontological species concept • Ecological species concept • The phylogenetic species concept

  26. Speciation occurs in one of two ways • Allopatric • Sympatric

  27. Allopatric speciation • population divided into geographically isolated subpopulations • Regions with many geographic barriers typically have more species • Even if contact is restored between populations, interbreeding is prevented

  28. Sympatric speciation • takes place in geographically overlapping populations • appearance of new ecological niches • Sexual selection • Polyploidy

  29. Autopolyploid

  30. Allopolyploid

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