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Evolution of Populations: Genes, Variation, and Speciation

This chapter explores the relationship between genetics and evolutionary thought, emphasizing the importance of populations in the process of evolution. It covers topics such as allele frequencies, genetic equilibrium, gene flow, genetic drift, sources of genetic variation, types of selection, artificial selection, sexual selection, speciation, and patterns of evolution.

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Evolution of Populations: Genes, Variation, and Speciation

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  1. Chapter 16: Evolution of Populations 16.1 Genes and Variation 16.2 Evolution as Genetic Change 16.3 The Process of Speciation

  2. Population Genetics • Evolutionary thought today is tightly linked to genetics. • Remember, populations, not individuals evolve. • All the alleles in a pop. added together are called thegene pool.

  3. Blue People of Kentucky

  4. Population Genetics • The frequency that any one allele is seenin the population is called theallele frequency (relative frequency). • Is the frequency of the dominant Huntington’s allele high? • Is the frequency of the dominant allele causing 6 fingers high?

  5. Population Genetics • If the frequency of the alleles doesn’t change over time, thepopulationisatgenetic equilibrium. • Hardy-Weinberg Principle • see page 401

  6. Population Genetics • When alleles are brought in and outof apopulationdue to migration ofindividuals, it is calledgene flow.

  7. Population Genetics • When isolated chance events can alter gene frequencies in a population (therefore disrupting gene equilibrium) you have what is called genetic drift. • Common in small isolated populations such as the Amish of Lancaster, PA • Darwin’s finches (perhaps) • founder effect: change as a result of migration

  8. Population Genetics • Sources of Genetic Variation: • Mutations • Gene Shuffling • Single gene trait • Polygenic trait

  9. Population Genetics • Types of selection: • When natural selection of a trait favors the average individuals in the pop. it is calledstabilizing selection.

  10. Population Genetics • Types of selection:  • When natural selection favors both extreme phenotypes of a trait in a pop., it is called disruptive selection.

  11. Population Genetics Types of selection:  • When natural selection favors one extreme phenotype of a trait, it is called directional selection.

  12. Population Genetics • Type of Selection?? • Grey mice are preyed upon but black and white mice are left alone? • The longer a giraffe’s neck gets the more food is available, while short necked giraffes die of starvation before they can reproduce? • A slow gazelle is easily caught by a cheetah, but one too fast breaks its legs easily and is eaten by hyenas?? Disruptive Directional Stabilizng

  13. Population Genetics • Artificial Selection: Selection for traits that are determined and monitored by man. • Ex. Breeding animals such as dogs or cats. • Sexual Selection: Selection by one gender for another gender. • Ex. Peacock feathers, body hair disappearance in humans, walrus tusks.

  14. Speciation • Speciationis when a new species is formed. This means that the individuals in the new species can no longer produce successful offspring with the population from which they came.

  15. Speciation • Geographic Isolationcan cause speciation over long periods of time. • The seperated organisms areadapting to different environmentsand responding differently. • Eventually if a mating is attempted, they can no longer produce successful offspring with one another.

  16. Speciation • Reproductive Isolationis when a population can no longer successfully interbreed with its parent population (the pop. it came from). • Reproduction if attempted will fail. • Ex. One group breeds in the fall, one in the spring and over time the populations become new species incapable of interbreeding. • Mating Calls • Courtship rituals differ

  17. Speciation • Temporal Isolation: • Two or more species reproduce at different times • Example: orchid in the rainforest

  18. Speciation • Changes in chromosome number can cause speciation. • Some cases ofpolyploidy(more common in plants) produce individuals that can only mate with other polyploids in a pop.

  19. 17.4 Speciation • Can occur rapidly • Punctuated Equilibrium • Gould • Can occur very slowly • Gradualism • Darwin • see page 439

  20. 17.4 Patterns of Evolution • Adaptive Radiation: When an ancestral species evolves into several different species, each filling a specific niche. • Darwin’s finches • Hawaiian Honeycreepers (p. 406 &436).

  21. 17.4 Patterns of Evolution • Divergent Evolution: Species that once were similar or closely related become very different. • New Species are very different from each other. • Ex. Adaptive Radiation

  22. 17.4 Patterns of Evolution • Convergent Evolution:Unrelatedspecies that live in similar environments evolve the same adaptations in order to survive. • Ex. Tasmanian Wolf and North American Wolf. • P. 437

  23. Patterns of Evolution • Coevolution: the process by which two species evolve in response to changes in each other over time. • Example: flowering plants and their pollinator • Page 437 http://biology.clc.uc.edu/courses/bio303/coevolution.htm

  24. 17.4 Note • Common genetic occurrences we have studied such as polyploidy, crossing over, andpoint mutationscan provide the genetic basis for evolution. Although these genetic changes are not evolution themselves, they can begin the long process of evolution by affecting one individual in a population in a positive way. But only if the trait is passed on, and on, andon…

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