Population Genetics

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
Genetic Drift
Gene Flow
Natural Selection
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
Two main types:
1.Founder effect
2.Bottle neck effect
Random change in the
gene pool that occurs
in a small colony of a
Founder Effect
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.
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
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.
The transfer of alleles into or
out of a population due to
movement of fertile
individuals or their
For example - movement of
pollen by wind or insects;
movement of humans
around the globe
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?
Genetic modifications from transgenic plants
passed to neighboring populations of wild
relatives. What type of event occurred?
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
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
Which type of event explains the high
incidence of polydactylism found in the
Amish population?
Reduction in geographic variation in the
appearance of humans is caused by what
type of event?