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Chapter 13- How Populations Evolve

Artificial selection Biogeography Bottleneck effect Comparative anatomy Comparative embryology Descent with modification Directional selection Diversifying selection Evolution Evolutionary adaptations Fitness Fossil record Founder effect Gene flow Gene pool. Genetic drift

mireille-clarke
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Chapter 13- How Populations Evolve

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  1. Artificial selection Biogeography Bottleneck effect Comparative anatomy Comparative embryology Descent with modification Directional selection Diversifying selection Evolution Evolutionary adaptations Fitness Fossil record Founder effect Gene flow Gene pool Genetic drift Hardy-Weinberg equilibrium Homologous structures Microevolution Modern synthesis Molecular biology Mutation Natural selection Neutral variation Population Population genetics Sexual dimorphism Species Stabilizing selection Chapter 13- How Populations Evolve

  2. Evolution • Change over time • Darwin called evolution- descent with modification until last paragraph of The Origin of Species

  3. Evolutionary adaptations • Inherited traits that increase an organism’s ability to survive and reproduce in a particular environment

  4. Fossil record • Ordered specimens in layers of sedimentary rock • Gives an idea of when certain adaptations appear • Younger fossils are on top of older ones

  5. Biogeography • Geographic distribution of species

  6. Comparative anatomy • Comparing body structures • Homologous structures- features with similar structure but a different function • Due to similar ancestry

  7. Comparative embryology • Study of structures that appear during development • Shows common ancestry in vertebrates

  8. Molecular biology • Study of molecular basis of genes and gene expression • Universal genetic code= life is related • Similar DNA and proteins= close relationships

  9. Darwin’s Theory points: • Overproduction • Competition • Variety • Adaptations • Natural selection • Speciation

  10. Artificial selection • Selective breeding of plants and animals

  11. Natural selection • Unequal reproductive success • Those that are better adapted to the env are more likely to survive, reproduce • Mechanism for evolution

  12. Natural selection in action: • Galapagos finches- avg. beak size differs in wet vs. dry years • Insecticide resistance- resistant insects survive and reproduce, next generation more are resistant • Antibiotic resistance- similar to insecticide resistance • Industrial melanism- moth coloring due to industrialization in England

  13. Population • Smallest unit that can evolve • Group of individuals of the same species living in the same place at the same time • Population genetics- science of genetic change in populations

  14. Population vocab • Modern synthesis- theory of evolution that includes genetics • Species- group of populations whose individuals can reproduce and produce fertile offspring

  15. Gene pool • Collection of genes (alleles) in a population at any given time • Frequency of alleles can change • Microevolution- change in gene pool over a few generations • Gene pools will remain constant if the population isn’t evolving – IMPOSSIBLE!!

  16. Hardy-Weinberg Equilibrium • Frequency of each allele in the gene pool will remain constant unless acted on by other agents • p2 + 2pq + q2 = 1 • freq. WW + freq. Ww + freq. ww = 1 • Used in human genetics to estimate how many people carry alleles for certain inherited diseases

  17. 5 conditions for H-W equilibrium • Large population • Pop. is isolated, no migration of individuals or gametes in or out • Mutations don’t alter gene pool • Random mating • All individuals are equal in reproductive success; natural selection does NOT occur • IMPOSSIBLE

  18. Causes of microevolution • Natural selection • Genetic drift- change in gene pool due to change • Bottleneck effect- random, drastic reduction of population size (ex: flood, earthquake) • Founder effect-colonization of a new location by a small # of individuals (ex: birds fly to new island)

  19. Causes of microevolution con’t • Gene flow- genes move into or out of a population (by fertile individuals or gametes) • Reduces genetic differences between pop.’s • Mutation- change in DNA, causes new alleles • ** ultimate source of genetic variation • Raw material for evolution

  20. Variation • Prevalent in most populations • Especially sexually reproducing species • Many traits are the result of several genes • Polymorphic- characteristic with 2 or more forms • ABO blood type • Can also happen in a cline- change in characteristic due to geography • As latitude increases, mammal/bird size increases • Is measured in gene or nucleotide diversity

  21. Variation con’t • Produced by sexual recombination and mutation • Most of the time it’s harmful, occasionally it creates a better variation • Asexual org’s- mutation generates • Sexual org’s- sexual recombination generates

  22. How natural selection affects variation • Heterozygote advantage- have greater reproductive success • Ex: malaria/sickle-cell • Balanced polymorphism- ability of natural selection to maintain 2 or more phenotypes • Neutral variation- no selective advantage (human fingerprints) • Endangered species have reduced variation • Why? Small gene pool

  23. Fitness • Relative contribution to gene pool of next generation • More fit- reproduce more have well-adapted young that reproduce • Fittest individual- passes most genes to next generation

  24. Outcomes of natural selection

  25. Outcomes of natural selection • Stabilizing- favors intermediates • Occurs in stable env’s • Prevails most of the time in populations • Directional- favors an extreme phenotype • Occurs during env. change or when there is migration to new habitat • Diversifying- favors both extremes • Can lead to balanced polymorphism • Occurs when habitat has 2 different env conditions

  26. Natural selection DOES NOT produce perfection, due to: • Historical constraints • Need to use already existing structures • Compromising for adaptations • Blue-footed booby- fast in water, clumsy on land • Not all evolution is adaptive • Chance happens, ex: bottleneck (could remove good genes) • Selection is only on existing variations

  27. Sexual selection may produce sexual dimorphism • Sexual dimorphism- distinction between secondary sex characteristics in males and females • Plumage, antlers, dances, manes • Intrasexual selection- fighting for females • Intersexual selection- mate choice, impressing other sex by dance, feathers etc • Many times it’s not advantageous to stick out to predators but it’s necessary for passing on genes

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