By: Becca Lencz, Ashley English, Nick Couto, Hillary Thorpe

A dramatic, often temporary, reduction in population size, usually resulting in significant genetic drift.

A dramatic reduction in population size (usually due to a natural disaster) New population’s genetic make up is not the same as the original population’s When population recovers, generations are limited to alleles carried by surviving individuals

Natural disaster such as: fire hurricane earthquake tsunami volcano tornado Population could also go through a dramatic reduction due to over hunting, poaching, disease, or a new predator.

A significant genetic drift Eliminated rare alleles from original population Rare alleles from original population become common Little genetic variation in population

Cheetahs have very little genetic variability. It is believed that they once belonged to a species that went through a dramatic genetic bottleneck event, where only seven individuals survived about years ago. Northern elephant seals passed through a genetic bottleneck event caused by hunting, its reduced their population size to as few as 20 individuals. There population has since rebounded to 30,000 but there traits still reflect the effects of the bottleneck event

Genetic drift that results when small number of individuals separate from their original population and establish a new population.

New population is then created New Colony is formed by few members of the original population

A group of individuals from the original population get separated and start a new colony Mainly happens when individuals from a species travel to a new island or continent

Reduced genetic variation from original population A new population created (new species) Rare Alleles become common

A large population of Dutch settlers in South Africa descended from only a few colonists. Much of this population has Huntington’s Disease because those few colonists happened to have an unusually high frequency of the disease.

The reason why these two types of genetic drifts are classified differently is because of the events leading to the reduction of the original population Genetic Bottleneck – a dramatic, temporary reduction in population Founder Effect – the separation of a small amount of individuals creating a new population

In natural selection the genes with the best survival qualities are the ones that get passed on to the next generation. In the founder effect or genetic bottleneck, the genes that get passed on aren't necessarily any better than the ones that got eliminated, they were just passed on by chance.