1. How does genetic drift affect the diversity of a population?
MT: Evolution

2. DNA frequency in a population changes simply by CHANCE not fitness
Genetic Drift
DNA frequency in a population changes simply by CHANCE not fitness
Survivors are lucky, not more fit
Deceased are unlucky, not less fit

3. Causes of Genetic Drift
Random events:
1. natural disasters – hurricane, volcano, tsunami, earthquake, fire, etc
2. stepped on, ran over, picked up, put on a boat, stuck in a car, stuck to fur or clothing
3. at the wrong place at the wrong time

4. some individuals of a population colonize a new habitat
Types of Genetic Drift
1. Founder’s Effect
some individuals of a population colonize a new habitat
2. Bottleneck Effect
few survivors are left to reproduce

5. Founder's Effect:
some individuals of a population colonize a new habitat
ex: Columbus bringing organisms to USA
S. America: DNA Frequency
25% pink
75% red
Spain: DNA Frequency
66% pink
33% red

6. After Katrina: DNA Frequency
Bottleneck Effect:
few survivors are left to reproduce
ex Hurricane Katrina
survivors!
Before Katrina: DNA Frequency
66% pink
33% red
After Katrina: DNA Frequency
40% pink
60% red

7. How does genetic drift affect the diversity of a population over time?

8. Genetic drift decreases diversity
Genetic drift decreases diversity. In this case yellow and pink DNA are gone, and red DNA is now the majority.
Genetic drift = decrease in DNA diversity

9. Let's Do This Together:
Did this population of Rivasitus undergo genetic drift after a tornado killed all except one X and one O?
Allele frequency of Original Population:
13/26 X's = 50%
13/26 O's = 50%
Allele frequency of New Population:
1/2 X's = 50%
1/2 O's = 50%
X O
X O O X X X O O O O
X X X X
X X X X X O
O O O O O O
survivors!

10. NO DNA frequency the SAME before and after! Let's Do This Together:
Did this population of Rivasitus undergo genetic drift?
Original Population:
13/26 X's = 50%
13/26 O's = 50%
New Population:
1/2 X's = 50%
1/2 O's = 50% NO
DNA frequency
the SAME
before and after!
X O O X X X O O O O
X X X X
X X X X X O
O O O O O O
X O

11. You Try: Allele Frequency of Original Population:
Did this population of Rivasitus undergo genetic drift?
Allele Frequency of Original Population:
__/__ X's = ___%
__/__ O's =___%
Allele Frequency of New Population:
__/__ X's = __%
__/__ O's = __%
X O O X X X O O
X X
X X O
O O O
XOXX O

12. different before and after!
YES!
DNA frequency
different before and after!
You Try:
Did this population of Rivasitus undergo genetic drift?
Original Population:
8/16 X's = 50%
8/16 O's =50%
New Population:
3/5 X's = 60%
2/5 O's = 40%
XOXX O
X O O X X X O O
X X
X X O
O O O

13. What does genetic drift do to the diversity of a population?
If genetic drift occurred on a population, and then there was a large change in their environment, how would the population be affected?
Critical Questions