Population Genetics

Terminology Population - a localized group of individuals capable of interbreeding and producing fertile offspring   Gene Pool - all of the alleles for all genes in all individuals of the population

Major factors that alter allele frequency Genetic Drift   Gene Flow Natural Selection

Genetic Drift These are chance events that cause allele frequencies to fluctuate unpredictably from one generation to the next   Tends to reduce genetic variation through losses of alleles Two main types: Founder effect Bottle neck effect

In addition to natural selection, genetic drift & gene flow cause change Random change in the gene pool that occurs in a small colony of a population 1814 – 15 people founded a British Colony on Tristan da Cunha. One person carried a recessive allele for retinitis pigmentosa (progressive form of blindness). In the 1960’s the island descendants were samples – of 240 individuals, 4 had the disease. The frequency for the disease is much higher among islanders than the area from which the founders came. Founder Effect Example

Bottleneck Effect A sudden change in the environment (flood / fire) that drastically reduces the population size; In the surviving population certain alleles may be over or under represented  

Bottleneck example Northern Elephant Seals were heavily hunted by man in the early 19th century reducing their population size to about 20 individuals.  Today the population has rebounded to over 30,000 but the effects of the bottleneck are evident in their DNA.  There is little genetic variation among this population when compared to a population of Southern Elephant seals that were not heavily hunted.

Gene Flow The transfer of alleles into or out of a population due to movement of fertile individuals or their gametes   For example - movement of pollen by wind or insects; movement of humans around the globe

Bottleneck, Gene Flow or Founder Effect? Flower population: ww = white flower; WW and Ww = purple flower; a mud slide wipes out most of the white flowered plants. What type of event occurred?

Bottleneck, Gene Flow or Founder Effect? Genetic modifications from transgenic plants passed to neighboring populations of wild relatives. What type of event occurred?

Bottleneck, Gene Flow or Founder Effect? Millions of greater prairie chickens once lived on the prairies of Illinois. As these prairies were converted to farmland and other uses during the 19th and 20th century, the number of greater prairie chickens plummeted to less than 50 individuals. The few survivors have low levels of genetic variation. What type of event occurred?

Bottleneck, Gene Flow, or Founder Effect? This event resulted in the world wide spread of several insecitcide-resistance alleles in the mosquito Cluex pipiens, a vector for West Nile virus and Malaria. What type of event occurred?

Bottleneck, Gene Flow or Founder Effect? Which type of event explains the high incidence of polydactylism found in the Amish population?

Bottleneck, Gene Flow, or Founder Effect? Reduction in geographic variation in the appearance of humans is caused by what type of event?