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Evolution in Action
Founder effect
The Founder Effect
An extreme form of genetic drift combined with the bottleneck effect is called the founder effect.

If a small number of individuals are separated from the original population, and the conditions are right, the smaller group can go on to form a new breeding population of their own, and thus start (or "found") a whole new species.


Two peccaries have got lost and separated permanently from their family herd by a flash flood. Luckily, one of these peccaries is a male with the genotype bb, and the other is a female with the genotype Bb.

On their own, and unable to rejoin the larger group, these two begin to breed and build a new herd. But the gene pool in this new founder population is very different from that seen in the original family herd.

The B gene has a frequency of 0.25, and the b gene has a frequency of 0.75. From these two peccaries, the new offspring will also have very different ratios of genotypes:

0.5 B 0.5 b
Sperm 0.5 b 0.25 Bb 0.25 bb
0.5 b 0.25 Bb 0.25 bb

Genotype Bb will have a frequency of 0.5 in the offspring.
Genotype bb will have a frequency of 0.5 in the offspring.

These are very different genotype frequencies from those found in the original population.

When a small number of individuals of any species are isolated from other members of the species because of loss, catastrophe, physical barriers, or migration, their own unique genotypes will then become the basis of a brand new gene pool.

New colonies that arise from the isolated individuals will have genotype frequencies very different from the original population.

New populations that arise from the founder effect clearly have different evolutionary potentials from the original populations. Isolated from other members of the same species, the forces of natural selection shape the different gene pools in different ways, often to fit very different environments.

Founder populations are usually very small; therefore, change can be quite rapid and these populations can accumulate new adaptations much faster than large populations.

Figure legend: Founder effect. From an original peccary population with its own gene pool, a few individuals survive a catastrope. These individuals become the founders (originators) of a new peccary population.

As they reproduce, the new gene pool is very different from that of the original population.

© 2001, Professor John Blamire