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Genetic Drift

Genetic Drift. By Bryce Perry and Cecil Brown. Genetic Drift vs. Natural Selection. How does natural selection work? Adaptation Selection of new beneficial traits according to selective pressures at the time

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Genetic Drift

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  1. Genetic Drift By Bryce Perry and Cecil Brown

  2. Genetic Drift vs. Natural Selection • How does natural selection work? • Adaptation • Selection of new beneficial traits according to selective pressures at the time • Natural selection produces adaptation of an organism to its environment, genetic drift only will cause a change in the allele frequencies

  3. Genetic Drift vs. Natural selection (cont.) • So, how does genetic drift work? • First off, we have to violate the Hardy-Weinberg equilibrium model • Limited population sizes • The other important point is that of sampling error

  4. Sampling Error • Sampling Error is defined as a random discrepancy between theoretical expectations and the actual results. • Occurs because the populations are finite and small

  5. Sampling Error (cont.) • Selection is differential reproductive success that happens for a reason, genetic drift is differential reproductive success that just happens. • Genetic drift is evolution that simply happens by chance due to sampling error.

  6. RANDOM FIXATION • Allele frequencies can drift between 0 and 1. • At 0 that frequency is lost • At 1 the allele is said to be fixed. Why is that? • Fixation is the elimination from a population all the alleles at a locus but one.

  7. WHAT IS HETEROZYGOSITY? • WHAT EFFECT DOES GENETIC DRIFT HAVE ON HETEROZYGOSITY?

  8. Population Evolutionary Paths • Why it is said that every population follows a unique evolutionary path?

  9. Population Size • What happens with a large population? • Lots of variation • Genetic drift is less powerful • What happens with a small population? • Genetic drift is very powerful • Loss of variation

  10. WHAT IS THE FOUNDER EFFECT?

  11. Founder hypothesis, is the hypothesis that many speciation events begin when small population colonize new geographic areas. • Founder event is the establishment of a new population usually by a small number of individuals.

  12. WHAT IS THE BOTTLE NECK EFFECT?

  13. SEWALL WRIGHT EQUATION • The probability of one allele drifting to fixation is given by the formula Number of copies of allele Total number of gene copies

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