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What Drives Evolution?

What Drives Evolution?. Mutations Genetic Drift Gene Flow Natural Selection. Gene Pool. Gene pool : collectively, all of the alleles of the population’s genes Allelic frequency : the percentage of any specific allele in the gene pool

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What Drives Evolution?

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  1. What Drives Evolution? • Mutations • Genetic Drift • Gene Flow • Natural Selection

  2. Gene Pool • Gene pool: collectively, all of the allelesof the population’s genes • Allelic frequency: the percentage of any specific allele in the gene pool • Genes can enter and leave a population’s gene pool for many reasons • Populations in which the gene pool is not changing are said to be in genetic equilibrium

  3. Example – Allelic Frequency • In a population, there are 100 individuals. Since each of them would have two alleles for a particularcharacter (trait), the total number of genes in this population is • 200 (=100 x 2). • 30 homozygous for the dominant trait (AA) • 50 are heterozygous (Aa) • 20 are homozygous for the recessive trait (aa). • The total number of dominant genes in the population is • (30 x 2) + (50 x1) = 110. • The frequency of the dominant trait (A) is • (110/200) = 0.55 or 55%. • The total number of recessive genes in the population is • (20 x 2) + (50 x 1) = 90. • The frequency of the recessive trait (a) is • (90/200) = 0.45 or 45%.

  4. Mutations • New genes can be added to the population by errors in DNA copying called mutations • Most mutations are BAD!

  5. Mutations • Very very rarely a mutation might come along that improvesan organism’s chance at survival or reproduction • These mutant genes will be passed along to offspring and become more common in the gene pool over time • If the mutation offers a large advantage, eventually (after many generations) all members of the population will have the beneficial mutation

  6. Genetic Drift • Genetic drift: when allelic frequencies are changed by random events in a isolated population

  7. Gene Flow • Gene flow: the transport of genes by traveling individuals • When an individual leaves a population, its genes are lost from the gene pool - emigration • When an individual enters a population, its genes are added to the gene pool - immigration

  8. Speciation • A certain population may become isolated and evolve to fit new or different environmental conditions • The isolated population my change so much that it can no longer mate with the original population • Speciation– the evolution of a new species

  9. Speciation • There are several reasons why similar populations no longer breed, creating new species: • GeographicIsolation leads to: • ReproductiveIsolation

  10. Reproductive Isolation • Geographic isolation: when a physical barrier divides a population preventing them from mating • E.g. Canyon, lava flow, continental drift • EcologicalIsolation: populations occupy different habitats and never encounter each other to mate • E.g. Population of monkeys that lives on the ground does not mate with tree dwelling monkeys • TemporalIsolation – Populations reproduce at different times of the year • E.g. Population of frogs that mate in March do not reproduce with frogs that mate in June

  11. North rim of Grand Canyon South rim of Grand Canyon

  12. Two Types of Evolution • Divergent evolution: species that once were similar become increasingly different • Happens when populations adapt to differentenvironments

  13. Two Types of Evolution • Convergentevolution: distantly related organisms evolve to become more similar • Happens when unrelated species adapt to similarenvironments, possibly in different parts of the world

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