Biology - Chp 16 - Evolution of Populations - Notes

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Biology - Chp 16 - Evolution of Populations - Notes

  1. 1. Chapter 16 Evolution of Populations 1
  2. 2. 16-1 Genes and Variation• As Darwin developed his theory of evolution, he worked under a serious handicap• He didn’t know how heredity worked• This lack of knowledge left two big gaps in Darwin’s thinking1.______________________________________________________________________________________________________________________________________________2.______________________________________________________________________________________________________________________________________________________________________________________________________________________• During the 1930’s Evolutionary biologists connected Mendel’s work to Darwin’s• By then biologists understood that genes control heritable traitsHow Common Is Genetic Variation?• Many genes have at least ________ forms or alleles• Animals such as horses, dogs, mice, and humans often have ____________________ alleles for traits such as body size or coat colorVariation and Gene Pools• Genetic variation is studied in populationsPopulation - ____________________________________________________________________________________________________________________________________• Because members of a population interbreed, they share a common group of genes called a gene poolGene pool - ______________________________________________________________ 2
  3. 3. ________________________________________________________________________Relative frequency - _______________________________________________________________________________________________________________________________________________________________________________________________________• In genetic terms, evolution is any change in the relative frequency of alleles in a populationSources of Genetic Variation• The 2 main sources of genetic variation are ________________________________ and the ________________________________________ that results from ____________________________________________________________Mutations - _____________________________________________________________• Mutations can occur because of o o• Some mutations don’t affect the phenotype but some doGene shuffling during sexual reproduction• Mutations are not the only source of variation• Most heritable differences are due to gene shuffling that occurs during the production of _________________________________• The 23 pairs of chromosomes can produce ______________________________ different combinations of genes• _________________________________ further increases the number of different genotypes that can also appear in offspring 3
  4. 4. Single – Gene and Polygenic Traits• The number of phenotypes produced for a given trait depends on how many genes control the traitSingle – gene trait - ______________________________________________________________________________________________________________________________• Variation in these genes leads to only 2 distinct phenotypesPolygenic traits - ________________________________________________________________________________________________________________________________• Each gene of a polygenic trait has 2 or more alleles• As a result one polygenic trait can have many possible genotypes and phenotypesEx.) height 4
  5. 5. Name _______________________________ Date _____________________ Per ______ 16 – 1 Section Review1. What two processes can lead to inherited variation in populations?2. How does the range of phenotypes differ between single-gene traits and polygenic traits?3. What is a gene pool? How are allele frequencies related to gene pools? 5
  6. 6. 4. How could you distinguish between a species in which there is a lot of variation and two separate species?5. How does the process known as independent assortment relate to the genetic variation that results from sexual reproduction? 16 – 2 Evolution as Genetic Change• A genetic view of evolution offers a new way to look at key evolutionary concepts• If each time an organism reproduces, it passes copies of its genes to its offspring…• We can therefore view evolutionary fitness as an organism’s success in passing genes to the next generation• We can also view an evolutionary adaptation as any genetically controlled physiological, anatomical, or behavioral trait that increases an individuals ability to pass along its genes• Remember that evolution is any change over time in the relative frequency of alleles in a population. This reminds us that it is populations, not individual organisms that can evolve overtimeNatural Selection on Single – Gene Traits• Natural selection on single gene traits can lead to changes in allele frequencies and thus to evolution 6
  7. 7. Natural Selection on Polygenic Traits• Natural selection can affect the distributions of phenotypes in any of three ways1. Directional Selection - ___________________________________________________________________________________________________________________________________________________________________________________________________ 7
  8. 8. 2. Stabilizing Selection - ___________________________________________________________________________________________________________________________________________________________________________________________________ 8
  9. 9. 3. Disruptive Selection - ___________________________________________________________________________________________________________________________________________________________________________________________________• Can create 2 distinct phenotypesGenetic Drift• Natural Selection is not the only source of evolutionary change• In small populations, an allele can become more or less common by chance 9
  10. 10. Genetic Drift - ___________________________________________________________Q: How does genetic drift take place?A:• These individuals may carry alleles in different relative frequencies than did the larger population from which they came• If so, the population that they found will be genetically different from the parent population• This cause is not natural selection, but _____________________________Founder effect - __________________________________________________________________________________________________________________________________________________________________________________________________________Evolution vs. Genetic Equilibrium• To clarify how evolutionary change operates, scientists often find it helpful to determine what happens when no change takes placeHardy – Weinberg principle - _______________________________________________________________________________________________________________________________________________________________________________________________Genetic equilibrium - ______________________________________________________ 10
  11. 11. ________________________________________________________________________• Five conditions are required to maintain genetic equilibrium from generation to generation1.2.3.4.5.Name _______________________________ Date ______________________ Per _____ 16 – 2 Section Review1. Describe how natural selection can affect traits controlled by single genes.2. Describe three patterns of natural selection on polygenic traits. Which one leads to two distinct phenotypes?3. 3. How does genetic drift lead to a change in a population’s gene pool? 11
  12. 12. 4. What is the Hardy-Weinberg principle?5. How are directional selection and disruptive selection similar? How are they different? 16 – 3 The Process of Speciation• Factors such as natural selection and chance events can change the relative frequencies of alleles in a population• But how do these changes lead to speciation?Speciation - _____________________________________________________________Isolating Mechanisms• Since members of the same species share a common gene pool, in order for a species to evolve into 2 new species, the gene pools must be separated into 2• As new species evolve, populations become reproductively isolated from each otherReproductive isolation - ____________________________________________________________________________________________________________________________Behavioral Isolation - ______________________________________________________________________________________________________________________________ 12
  13. 13. ________________________________________________________________________Geographical Isolation - ____________________________________________________________________________________________________________________________________________________________________________________________________Temporal Isolations - ______________________________________________________________________________________________________________________________Testing Natural Selection in NatureQ: Can evolution beobserved in nature?A:• Darwin hypothesized that finches had descended from a common ancestor and overtime, natural selection shaped the beaks of different bird populations as they adapted to eat different foods• The Grants, realized that Darwin’s hypothesis relied on two testable assumptions1.______________________________________________________________________________________________________________________________________________ 13
  14. 14. 2.______________________________________________________________________________________________________________________________________________Variation• The Grants identified and measured every variable characteristic of the birds on the island• Their data indicated that there is a great variation of heritable traits among the Galapagos finchesNatural Selection• During the…• Rainy season – ________________________________________________________• Dry season – __________________________________________________________• At that time, differences in beak sizes can mean the difference between life and death• Birds become feeding specialists• The Grants discovered that individual birds with different size beaks had different chances of survival during a droughtSpeciation in Darwin’s Finches• Speciation in the Galapagos finches occurred by founding of a new population, geographical isolation, changes in the new population’s gene pool, reproductive isolation and ecological competition 14
  15. 15. Founders Arrive• Many years ago, a few finches from South American mainland• Species A, flew or were blown to one of the Galapagos IslandsGeographic Isolation• Later on, some birds from species A crossed to another island in the Galapagos group• The finches then became unable to fly from island to island and become isolated from each other and no longer share a common gene poolChanges in the Gene Pool• Overtime, populations on each island became adapted to their local environmentsReproductive Isolation• Now imagine that a few birds from the second island cross back to the first islandQ: Will the population A birds, breed with thepopulation B birds?A:Ecological Competition• As these two new species live together in the same environment, they compete with each other for available seeds 15
  16. 16. • The more different birds are, the higher fitness they have, due to __________________________________Continued Evolution• This process of isolation on different islands, genetic change, and reproductive isolation probably repeated itself time and time again across the entire Galapagos island chain• Over many generations, it produced the 13 different finch species found there todayStudying Evolution Since Darwin• It is useful to review and critique the strength and weakness of evolutionary theory• Darwin made bold assumptions about heritable variation, the age of the Earth, and the relationships among organisms• New data from genetics, physics, and biochemistry could have proved him wrong on many counts, and ____________________________• Scientific evidence supports the theory that living species descended with modification from common ancestors that lived in the pastLimitations of Research• The Grants data shows how competition and climate change affects natural selection• However, they did not observe the formation of a new speciesUnanswered Questions• Many new discoveries have led to new hypotheses that refine and expand Darwin’s original ideas• No scientist suggests that all evolutionary processes are fully understood. Many unanswered questions remainWhy Understanding Evolution is Important?• Evolution continues todayEx.) o 16
  17. 17. o• Evolutionary theory helps us understand and respond to these changes in ways that improve human lifeName _________________________________ Date _____________________ Per ____ 16 – 3 Section Review1. How is reproductive isolation related to the formation of new species? 17
  18. 18. 2. What type of isolating mechanism was important in the formation of different Galápagos finch species?3. Explain how behavior can play a role in the evolution of species.4. Leopard frogs and tree frogs share the same habitat. Leopard frogs mate in April; tree frogs mate in June. How are these species isolated from each other? 18

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