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SAC 2 (Revision)

SAC 2 (Revision). Evolutionary relationships. Focus of the task. Key knowledge: Change in populations: gene pool, allele frequencies, selection pressures, genetic drift Natural selection as a mechanism of evolution Geological time: scale, relative and actual dating techniques

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SAC 2 (Revision)

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  1. SAC 2 (Revision) Evolutionary relationships

  2. Focus of the task Key knowledge: • Change in populations: gene pool, allele frequencies, selection pressures, genetic drift • Natural selection as a mechanism of evolution • Geological time: scale, relative and actual dating techniques • Patterns of evolution: divergent, convergent, allopatric speciation, extinction • The development of evolutionary theory • Evolutionary relationships: conservation of genes, phylogeny, mitochondrial evolution

  3. Section A: Darwin’s finches

  4. Charles Darwin • Came up with the theory of evolution by means of natural selection. • Famous for the Galapagos finches that he observed on the Galapagos islands- various species of finches (different features- beak shapes)

  5. Darwin’s investigation • Darwin investigated and observed many different species and noticed variations. • He wondered how the variations came about? HE noticed similarities. • Darwin concluded that: • Differences (genetic variation) between individuals determine how well they will survive (fitness). • Traits that increase the possibility of an organism’s survival are passed onto offspring(heritable).

  6. Natural Selection in a Nutshell! • As populations of living things expand, generation by generation, they will inevitably run into limits: limits on food, space or the right kind of habitat • These natural pressures limit or determine which individuals are able to survive and reproduce (i.e. fitness levels) • Not all individuals in a population are exactly alike • Some will have traits that give them an advantage in surviving, mating & passing on their traits to the next generation • These differences are known as variation (i.e. genetic variation) • A change in any aspect of the environment can suddenly turn what had been just another variation or variant into either an advantage or a disadvantage • If a selective pressure (i.e. change in the environment), acts against or upon the differences between the individuals in a population, you get natural selection, which, through time, can cause a population to evolve(change)

  7. Natural Selection as the mechanism for EVOLUTION • Natural selection = 'survival of the fittest’ • It is the process by which nature selects better adapted individuals for more successful reproduction. • Natural selection operates on individuals, but it is the population that evolves!

  8. VARIATION SELECTION EVOLUTION occurs after MANY GENERATIONS VARIATION SELECTION RESULT

  9. Divergent Evolution • Relatedorganisms (species with the same ancestor) become more and more DIFFERENTuntil they are a different species!

  10. Convergent Evolution • Unrelated organisms (species with different ancestors) evolve similar adaptations in response to their environment.

  11. Relatedness

  12. Techniques for determining relatedness • DNA-DNA hybridisation

  13. Section B: Evolutionary Relationships Investigation

  14. Cladograms

  15. Homologous & Analogous Structures Homologous- similar structure • Same general structure but different functions, e.g. wing of a bird, wing of a bat, leg of crocodile, flipper of whale & arm of human • Organisms with homologous structures have a common ancestor. Analogous- similar function • Not necessarily similar in basic structure, e.g. a fly’s wing and a bat’s wing. • Organisms with analogous structures have different ancestors.

  16. Absolute Dating Absolute age defines the actual age of the things. Radioisotope Dating: • works on the fact that radioactive isotopes decay (lose their radioactivity) in a predictable way, over periods of time. • The half life of a radioisotopes can be used to determine the age of a sample (rock or fossil)

  17. Absolute Dating Types of Radioisotopes: • Different radioisotopes have different half lives and are thus useful for dating different types of fossilised remains. • Carbon-14 works for fossils up to 40,000 years (there is 100% breakdown after 40,000 years) • Older fossils may be dated using different radioisotopes (i.e. Potassium-Argon has a half-life of 1.3 million years).

  18. Relative Dating Relative age refers to the age of something when compared to another thing. • Depends on stratification: the process of formation of layers in sedimentary rocks

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