Genetic Drift
Genetic drift is one of the four evolutionary forces in addition to natural selection,
mutations, and genetic flow. It describes the random change in allele frequency
over time. In other words the genetic change happens purely by chance . It can lead
to one allele being discarded (lost) or being fixed (the only allele on a gene). It has
the greatest impact on small populations that are endogamous (i.e. they mate
within the group). There are two types of genetic drift; founder effect and
bottleneck, as described below.
"The gene frequencies of one generation may be expected to differ a little from those of
the preceding merely by chance. In the course of generations this may bring about
important changes, although the farther the drift from the theoretical equilibrium, the
greater will be the pressure toward return." (Wright 1931b: 205; )
Founder
effect
Bottleneck
Causes
The bottleneck effect is usually the
result of a natural catastrophe, like an
earthquake, flood or volcano, but can
also be the result of human activity, .
The smaller group that survives is
significantly reduced in terms of
genetic variation and it no longer
represents the genetic makeup of the
original population.
Causes
The founder effect is the loss of
genetic variation due to migration by
a subset of individuals from a larger
parent population. The new founder
group no longer represents the
genetic variety of the original parent
group.
Effects
Effects
The very reduced population
leads to less genetic variation
and drift can happen. This could
lead to an allele being fixed or
lost. This can impact survivability
as organisms are less able to
adapt. Many endangered species
have been through a bottleneck.
The new group no longer represents the
parent group, as s result genetic
variation is limited and gene fixtion and
loss may occur. The small population
can lead to in-breeding which further
impacts genetic diversity and
precipitates disease. In extreme cases
speciation and a new species develops.
Example
In 1775 90% of the human population
lost their lives on the Micronesian
Island
of Pingelap,
in a shades
typhoon. One
Use
different
or
of the 20 survivors
had to
contrasting
colors
achromatopsia, a rare genetic
emphasize
the clear
syndrome
leading to colour
blindness
division
between
and sensitivity
to light. the
Aftertwo
6
generations 5% of
the population has
ideas.
this disorder, all descended from the
original survivor.
Examples
French settlers in Quebec between
1608 and 1760 now contribute 90% of
the gene pool in that province.
Both the French-speaking population
of Quebec and Ashkenazi Jews
experience a higher proportion of Ty
Sachs disease due to the founder
effect.
References
Larsen, C. S. (2022), The Essentials of Biological Anthropology (5th ed.) Norton.
Patil, K. B. (2020, March 12). Bottleneck Effect Vs. Founder Effect. Science
Stories. https://science.visualstories.com/bottleneck-effect-vs-founder-effect
Wright, S. (1931). Statistical Theory of Evolution. Journal of the American
Statistical Association, 26(173), 201–208. https://doi.org/10.2307/2277618