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 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
• Genetic drift that results when small
number of individuals separate from
their original population and establish
a new population.
New Colony
is formed by
few members
of the
original
population
New
population
is then
created
• 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.