Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Hardy-Weinberg Equilibrium In real populations, allele and genotype frequencies do change over time (Evolution!) The five conditions for non-evolving populations are rarely met in nature, but help us calculate allele frequencies. – 1)Extremely large population size – 2)No gene flow – 3)No mutations – 4)Random mating – 5) No natural selection How are your algebra skills???

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Population Genetics and Human Health We can use the Hardy-Weinberg equation to estimate the percentage of the human population carrying the allele for an inherited disease Three major factors alter allele frequencies and bring about most evolutionary change: – Natural selection (survival of the fittest) – Genetic drift – Gene flow

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Genetic Drift The smaller a sample, the greater the chance of deviation from a predicted result Genetic drift describes how allele frequencies fluctuate unpredictably from one generation to the next Genetic drift tends to reduce genetic variation through losses of alleles

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Bottleneck Effect The bottleneck effect is a sudden change in the environment that may drastically reduce the size of a population The resulting gene pool may no longer be reflective of the original population’s gene pool Cheetah – ice age Prairie chicken - hunting

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Founder Effect The founder effect occurs when a few individuals become isolated from a larger population It can affect allele frequencies in a population Ex: Amish in Pennsylvania, beetles on island

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Gene Flow Gene flow—also called migration—is any movement of genes from one population to another. Gene flow includes lots of different kinds of events, such as pollen being blown to a new destination or people moving to new cities or countries. If genes are carried to a population where those genes previously did not exist, gene flow can be a very important source of genetic variation. Native Americans and English.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Why Natural Selection Cannot Fashion Perfect Organisms Adaptations are often compromises (look how weird the human body is – tail bone) Chance and natural selection interact Selection can only edit existing variations so a lot of adaptations aren’t perfect they’re contrived!