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Mechanisms of Change

Mechanisms of Change. Natural Selection Genetic Drift Gene Flow Mutation Recombination. Gene Frequency Population Descent Gene Flow Genetic Drift Recombination Homozygous Heterozygous. Genotype Phenotype. Essential Vocabulary. Essential Question.

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Mechanisms of Change

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  1. Mechanisms of Change Natural Selection Genetic Drift Gene Flow Mutation Recombination EPISD Science

  2. Gene Frequency Population Descent Gene Flow Genetic Drift Recombination Homozygous Heterozygous Genotype Phenotype Essential Vocabulary EPISD Science

  3. Essential Question • What is responsible for both the remarkable similarities we see across all life and the amazing diversity of that life? • How does it work? EPISD Science

  4. Recap: What is evolution? • Descent with modification from a common ancestor. • Genetic variation is essential for selective forces to act upon in order for evolution to occur. EPISD Science

  5. Several generations later, brown beetles are more common and make up 70% of the population. Genetic Variation • What is being modified? • The gene frequency within a population over time. How did this happen? 90% of beetles in a population have the genes for bright green coloration, 10% have the genes for brown coloration. EPISD Science

  6. Mechanisms of change • Natural selectionImagine that green beetles are easier for birds to spot (and hence, eat). Brown beetles are a little more likely to survive to produce offspring. They pass their genes for brown coloration on to their offspring. So in the next generation, brown beetles are more common than in the previous generation. EPISD Science

  7. Mechanisms of change • Genetic driftImagine that in one generation, two brown beetles happened to have four offspring survive to reproduce. Several green beetles were killed when someone stepped on them and had no offspring. The next generation would have a few more brown beetles than the previous generation — but just by chance. These chance changes from generation to generation are known as genetic drift. EPISD Science

  8. Mechanisms of change • Gene Flow (Migration) Some individuals from a population of brown beetles might have joined a population of green beetles. That would make genes for brown coloration more frequent in the green beetle population than they were before the brown beetles migrated into it. EPISD Science

  9. Mechanisms of change • A mutation could cause parents with genes for bright green coloration to have offspring with a gene for brown coloration. That would make genes for brown coloration more frequent in the population than they were before the mutation. EPISD Science

  10. Mechanisms of change • Genetic Recombination sexual reproduction can introduce new gene combinations every generation into a population and is an important source of genetic variation. EPISD Science

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