1. By Bryce Perry and Cecil Brown
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