1. Genetic Drift DRIFT What do you think of when you see the word Drift?
Aimless (without direction)
DRIFT
Moving
Slow

2. Genetic Drift Random changes in allele frequency in a population
Example: population of Morgan Hill has 30% hitch-hiker’s thumb allele (B) in 1980, but 45% hitch-hiker’s thumb allele (B) in 2010.
This process is largely random, not necessarily influenced by adaptation.

3. Genetic drift Evolution by adaptation
Evolution drift based on the variation
Example:
100 humans= total population size
Blond + brown = color alleles
The random change in allele frequency over time is called genetic drift

4. Genetic drift
A small sample size of individuals always reduces the size

5. The Founder Effect Founder An extreme case of Genetic Drift
first
starter
An extreme case of Genetic Drift
When a small population breaks off from the bigger population and moves to live in a new place. (small population =new founders)
KEYPOINT = the founder effect leads to REDUCED GENETIC DIVERSITY.

6. founders of a new population
The Founder Effect
Why? Why does the founder effect reduce genetic diversity. . .
Because only the alleles in the small gene pool that broke off will exist in the new population.
founders of a new population
Lost the allele!

7. Founder Example: the Amish
Amish = good example of founders. Why? Because a small group isolated themselves (broke off from a big population) and set up colonies in Pennsylvania.
HIGH FREQUENCY of Ellis-van Creveld Syndrome (causes six-fingered dwarfism = short + 6 fingers)
Why? Because one of their founders, Samuel King, had the mutation and the Amish inbreed within their own population
Check for understanding: do all Amish have six fingers? Autosomal recessive

8. The child has shortened limbs and six fingers on each hand
The child has shortened limbs and six fingers on each hand. All the Amish with this syndrome are descendants of a single couple that helped found the Amish community in Lancaster County, Pennsylvania in Because of inbreeding in the isolated community, the recessive trait is now common

9. The Bottleneck Effect An extreme case of Genetic Drift
When a population decreases to a very small number (a lot die off) but then repopulates before it goes extinct.
KEYPOINT = the bottleneck effect leads to REDUCED GENETIC DIVERSITY.

11. The Cheetahs
Believed that around 10,000 years ago. . . almost all the cheetahs IN THE WORLD DIED except 7.
Those 7 repopulated the whole cheetah species.
Every cheetah is similar to all other cheetahs because they have only had 10,000 years of evolution. (humans have had at least 4 million)

12. Bottom Line
Extreme Genetic Drift (like the bottleneck or founder effects) _______________ genetic variation / genetic diversity.
DECREASES

13. Independent Practice
STOMP! it out