Mechanisms of Change Natural Selection Genetic Drift Gene

Mechanisms of Change Natural Selection Genetic Drift Gene Flow Mutation Recombination 10/30/2021 EPISD Science 1

Essential Vocabulary • • Gene Frequency Population Descent Gene Flow Genetic Drift Recombination Homozygous Heterozygous 10/30/2021 • Genotype • Phenotype EPISD Science 2

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? 10/30/2021 EPISD Science 3

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. 10/30/2021 EPISD Science 4

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. 10/30/2021 Several generations later, brown beetles are more common and make up 70% of the population. EPISD Science 5

Mechanisms of change 1. Natural selection Imagine 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. 10/30/2021 EPISD Science 6

Mechanisms of change 2. Genetic drift Imagine 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 10/30/2021 genetic drift. EPISD Science 7

Mechanisms of change 3. 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. 10/30/2021 EPISD Science 8

Mechanisms of change 4. 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. 10/30/2021 EPISD Science 9

Mechanisms of change 5. Genetic Recombination sexual reproduction can introduce new gene combinations every generation into a population and is an important source of genetic variation. 10/30/2021 EPISD Science 10