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