bottlenecks and founder effects

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

Bottlenecks and Founder Effects

Genetic Bottleneck

Definition

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

How It WorksA 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

Causes of Population ReductionNatural 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.

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

Diagram

Examples• 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 10 000 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

Founder Effect

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

How It Works

New population is then created

New Colony is formed by few members of the original population

Causes of the New Colony• 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

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

Diagram

Examples• 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.

Why Are They Classified Differently?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

How Are They Different From Natural Selection?• 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.

The End