AP Biology Big Idea #1 – Evolution Change in the genetic makeup of a population over time IS evolution. Adapted from Rebecca Rehder Wingerden ©

Evolution change is also driven by random processes. Genetic drift is a nonselective process occurring in small populations. Generation 1 p (frequency of CR) = 0.7 q (frequency of CW ) = 0.3 CR CR CR CR CR CW CW CW CR CR CR CW CR CR CR CW CR CR CR CW

Evolution change is also driven by random processes. Genetic drift is a nonselective process occurring in small populations. CR CR CR CR CR CR CR CR CR CW CR CW CW CW CR CR CW CW CR CR CR CW CR CW CR CR CR CR CR CW CR CW CR CR CR CW CR CR CR CW Generation 1 p (frequency of CR) = 0.7 q (frequency of CW ) = 0.3 Generation 1 p = 0.5 q = 0.5

Evolution change is also driven by random processes. Genetic drift is a nonselective process occurring in small populations. CW CW CR CR CR CR CR CR CR CR CR CW CR CR CR CR CR CW CR CR CR CR CR CR CW CW CW CW CR CR CR CW CR CR CR CR CR CW CR CR CW CW CR CR CR CR CR CW CR CR CR CR CR CW CR CW CR CW CR CR Generation 1 p (frequency of CR) = 0.7 q (frequency of CW ) = 0.3 Generation 2 p = 0.5 q = 0.5 Generation 3 p = 1.0 q = 0.0

Evolution change is also driven by random processes Evolution change is also driven by random processes. – The Bottleneck Effect Original Population Bottleneck Event Surviving Population

Evolution change is also driven by random processes Evolution change is also driven by random processes. – The Bottleneck Effect • Overhunting pushed the northern elephant seal to the brink of extinction by the late 19th century. •Though they have made a comeback, the genetic variation within the population remains very low.

Evolution change is also driven by random processes Evolution change is also driven by random processes. - The Founder Effect • British colony on Tristan da Cunha - high frequency of recessive allele for retinitis pigmentosa (progressive blindness).

Evolution change is also driven by random processes. Pre-bottleneck (Illinois, 1820) Post-bottleneck (Illinois, 1993) Evolution change is also driven by random processes. Range of greater prairie chicken B. Reduction of genetic variation within a given population can increase the differences between populations of the same species. - Illinois population drop in the number of alleles per locus and decrease in hatchlings (farming). - Kansas, Nebraska, Minnesota populations remained strong. (a) The Illinois population of greater prairie chickens dropped from millions of birds in the 1800s to fewer than 50 birds in 1993 Number of alleles per locus Percentage of eggs hatched Location Population Size Illinois 1930–1960s 1993 1K – 25K <50 5.2 3.7 93 <50 Kansas, 1998 (no bottleneck) 750K 5.8 99 Nebraska, 1998 (no bottleneck) 75K – 200K 5.8 96 Minnesota, 1998 (no bottleneck) 4K 5.3 85 Bozeman Biology: Genetic Drift(12:00 min.) http://www.bozemanscience.com/003-genetic-drift