1. Random Genetic Drift : Chance as an Evolutionary Force
Random Genetic Drift is the random change in allele frequencies from one generation to the next that is caused by the finite size of the breeding population of parents.
By chance, some parents have more offspring than other parents.
By chance, some parents have fewer offspring or no offspring at all.

2. Random Genetic Drift occurs in ALL countable, finite populations.
RGD is STRONGER in Small Populations (0 < N < 500).
RGD is WEAKER in Large Populations (500 < N).
The Strength of RGD is proportional to (1/2N) in a diploid population and to (1/N) in a haploid population.

3. The Strength of RGD is proportional to (1/2N) in a diploid population.
RGD is STRONGER in Small Populations (0 < N < 500). If N = 20 diploids, then (1/2N) = 0.025;
If N = 20 haploids, then (1/N) = RGD is always TWICE as strong for a haploid population of N individuals than a diploid population of the same size.
RGD is WEAKER in Large Populations (500 < N). If N = 2,000, then (1/2N) =

4. RGD and its Evolutionary Consequences
1) WITHIN populations RGD DECREASES GENETIC VARIATION :: Random Genetic Drift makes a population less genetically less variable and makes the individuals in the population more Homozygous.
The ultimate outcome: ALL HERITABLE VARIATION IS LOST!!
The population becomes either p* = 0.0 (allele is lost) or p* = 1.0 (allele is FIXED).
2) BETWEEN populations RGD INCREASES GENETIC VARIATION: Random Genetic Drift makes two populations become genetically different from one another.

5. Generation 1 Generation 2 5 5 No Chance Events 5 5 5 5 5 7
Frequencies
Stay Exactly
the Same 5 5 5 7
Chance Events 5 4
Random Genetic
Drift 5 4

6. Generation 1
Generation 2
Chance Events
Outcome 2 5 5 5 6 5 4

7. Generation 1
Generation 2
Chance Events
Outcome 3 5 3 5 6 5 6

8. Many Possible Outcomes
Generation 2
Random Genetic Drift
Different
Chance Events
Lead to
Different Outcomes 7 4
Generation 1 4 5 3 5 6 5 6 5
One Starting Point 6 4
Many Possible Outcomes

9. On Allele Frequencies = ZERO
Generation 1
Generation 2
Average of MANY
Independent
Chance Events 5 5 5 5 5 5
Average Effect of
Random Genetic Drift
On Allele Frequencies = ZERO
Average DP = 0
On AVERAGE
Frequencies
Stay the Same

10. Generation 1 Generation 2 5 5 No Chance Events 5 5 5 5 5
Frequencies
Stay Exactly
the Same 5 5 5
Random Genetic
Drift 7 5 4
On AVERAGE
Frequencies
Stay the Same 5 4

11. Q: If the frequency of an allele, B, at time 0, equals 0
Q: If the frequency of an allele, B, at time 0, equals 0.65, what is probability that RGD will result in LOSS of the B allele?
A) 0.00
B) 0.50
C) 0.65
D) 1.00
E) None of the above

13. RGD INCREASES Variation AMONG Populations
RGD for A Few
Generations
With NO
Migration
START: All Populations Genetically
Identical
END: Populations Genetically
Different from one another

14. RGD DECREASES Variation WITHIN Populations
RGD for Many
Generations
With NO
Migration
All Populations Genetically
Identical
Populations Genetically
Different from one another

15. All Populations Genetically Genetically Different
Migration opposes RGD and LIMITS its effects
RGD and Migration
for Many
Generations
All Populations Genetically
Identical
Populations Somewhat
Genetically Different

16. Random Genetic Drift : Effects on Populations
1. On average WITHIN a population, RGD DECREASES genetic variation:
A) Random Genetic Drift makes individuals more homozygous, more genetically similar.
B) the population becomes genetically less variable.
C) RGD causes FIXATION (Pa = 1) or LOSS (Pa = 0) of alleles.
D) RGD diminishes the heritable variation within a population for natural selection.
2. On average AMONG populations, RGD INCREASES genetic variation:
A) RGD makes different populations genetically more different from one another.
3. GENETIC FIXITY of SPECIES is NOT possible. There is continual change of allele frequencies in finite populations by chance, RGD.

17. Many Possible Outcomes
Generation 2
Random Genetic Drift 7
Different
Chance Events 4
Generation 1 4 5 3 5 6 5 6 5
One Starting Point 6 4
Many Possible Outcomes