Genetic drift is a change in allele frequencies in a population due to chance events, and is more likely to occur in small populations. Unlike natural selection, genetic drift is random and can cause changes in traits that are beneficial, detrimental, or neutral. Two types of genetic drift are founder effect, which occurs when a small group colonizes a new area, and population bottleneck, which is caused by a drastic reduction in population size, such as from a natural disaster.

1. Notes: Genetic Drift (pg 10)
• Genetic Drift = Change in allele frequencies in
a population due to chance events

2. Notes: Genetic Drift (pg 10)
• Genetic Drift = Change in allele frequencies in
a population due to chance events
• More likely to occur in small populations

3. Notes: Genetic Drift (pg 10)
• Genetic Drift = Change in allele frequencies in
a population due to chance events
• More likely to occur in small populations
• Unlike natural selection, which favors
beneficial traits, genetic drift is random and
can cause an increase in traits that are
beneficial, detrimental, or neutral

4. Types of Genetic Drift
1. Founder effect: Changes in gene frequency
due to colonization of a new area by a limited
number of individuals

5. Types of Genetic Drift
1. Founder effect: Changes in gene frequency
due to colonization of a new area by a limited
number of individuals
Example: British colony on Tristan da Cunha
island founded by 15 people. 1 colonist
carried an allele for a type of blindness.
Today, 2% of individuals on the island are
blind, compared to <0.01% in the general
population

6. 2. Population bottleneck: Change in gene
frequency caused by a drastic reduction in the
size of a population, usually due to a natural
disaster.

7. 2. Population bottleneck: Change in gene
frequency caused by a drastic reduction in the
size of a population, usually due to a natural
disaster or hunting
Example: Cheetahs. 2 Bottlenecks: 10,000 years
ago (ice age) and 1800’s (hunting). Now
cheetahs are very similar genetically, leading
to problems associated with inbreeding

8. Output activity (pg 11)
Imagine that a massive earthquake kills all
humans on Earth except for President Obama
and Vice President Biden and their families
(they were safely aboard Air Force One).
These 9 people will now repopulate the Earth

9. Output activity (pg 11)
Imagine that a massive earthquake kills all
humans on Earth except for President Obama
and Vice President Biden and their families
(they were safely aboard air force one). These
9 people will now repopulate the Earth
1. Are these people a representative sample of
human genetic diversity? Explain.
2.List at least 5genetic traits that would be lost
due to this population bottleneck