Bottleneck Effect In Human Population

TOPIC : BOTTLENECK EFFECT IN
HUMAN POPULATION

CONTENTS
Introduction
Genetic drift v/s Natural selection
Kinds of Genetic Drift
Bottleneck effect
Role of bottleneck effect in evolution
References

INTRODUCTION
Basic mechanisms of evolution (along with natural selection and mutation).
Random, stochastic process.
Independent of selection
“Random Drift" or “Random Genetic Drift" (allele frequencies do not change in any predetermined direction in this process)
“The change in the frequency of an allele in a population due to random
sampling of organisms.”

Common in small population, no significance in large population.
Some alleles become more common while others become less common over time (or lost).
When there is only one allele is left for a particular gene pool, that allele is said to be fixed.
Source: http://bio1151.nicerweb.com/Locked/media/ch23/drift.html

GENETIC DRIFT V/S NATURAL SELECTION
Genetic Drift
Random process
Doesn't occur due to environment challenges
Non directional
Non adaptive evolution
Important allele may disappear
Operate on neutral allele
Loss of genetic variation
Natural Selection
Non random process
Occur due to environment challenges
Directional
Generation of adaptive trait
Ends up with survival of fittest
Operate on any allele
Increase genetic variation

KINDS OF GENETIC DRIFT
Factors that cause genetic drift are:
Bottleneck Effect
Reduction in population size
Founder Effect
Subset of population founds new population

BOTTLENECK EFFECT
The bottleneck effect occurs when a natural disaster or similar event randomly kills a large portion (i.e. random sample) of the population, leaving survivors that have allele frequencies that were very different from the previous population.
Source: http://evolgen.wikispaces.com/Group+19?responseToken=ff19f377988e5706840fce1e021e0034

EXAMPLE OF A BOTTLENECK
11th July, 2015
Northern elephant seals
Bottleneck event
Humans hunting (1890s)
Population size 20 individuals (at the
end of the 19th century)
Now Population 30,000
— but their genes still carry the
marks of this bottleneck:
Much less genetic variation
Source: http://science.opposingviews.com/comparison-bottleneck-effect-founder-effect-5188.html

Affects the genetic makeup of the population.
Mechanism of evolution, doesn't work to produce adaptations.
Cause non-adaptive evolution
Allele fixing
Decreases gene diversity
New population genetically distinct from its original population
Plays a role in the evolution of new species
ROLE OF BOTTLENECK EFFECT IN EVOLUTION

REFERENCES
Pradeep's , A Text Book Of Biology class 12th ; G. Chopra,H.N. Srivastava,P.S. Dhami
Biology, A text book for class XII (NCERT)
Source: Boundless. “Genetic Drift.” Boundless Biology. Boundless, 21 Jul. 2015.
Retrieved 10 Sep. 2015 from
http://evolution.berkeley.edu/evolibrary/article/evo_24
http://www.apsnet.org/edcenter/advanced/topics/PopGenetics/Pages/geneticdrift.aspx
https://www.boundless.com/biology/textbooks/boundless-biology-textbook/the-evolution- of-populations-19/population-genetics-131/genetic-drift-531-11736/