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

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.

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

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

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.

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!

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

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 1744. Because of inbreeding in the isolated community, the recessive trait is now common

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.

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)

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

Independent Practice STOMP! it out