Genetic Drift – Definition and Examples

What is Genetic Drift?

Genetic Drift or genetic sampling error or Sewall Wright effect is nothing but a variation of change in the gene pool of a small population. It occurs strictly by chance and no other specific reasons.

In other words, we can say that Genetic Drift leads to evolution owing to chance events. Although we can find its effect to be the strongest in small populations. Nevertheless, it occurs in all populations of non-infinite sizes too.

As we all know that natural preference or natural selection plays a prominent part in the mechanism of evolution. But at times evolution takes place by chance too. In such cases, Genetic Drift takes place whether it makes the population better-suited for its environment or not.

We can also understand it as the change occurring due to the sampling error in the selection of the alleles. It happens in the upcoming generation from the gene pool of the current generation.

Examples of Genetic Drift

To exemplify the genetic drift, let’s take a hypothetical example of a population of 100 rabbits that live in the woods. All the rabbits in the woods have various colours of their coats.

The colours are black, grey, white, tan, brown and red. In the population of the rabbits, the alleles creating the coat colour are spread equally.

Suppose a disease comes into the population of those rabbits and due to this 98 rabbits die. The two rabbits which are left are brown and black. Now, we can say that there has been a Genetic Drift from 6 alleles to only 2 alleles.

It may be surprising to know, but the fact is that GD keeps on happening all the time in the populations. But we cannot easily see it. Many times mutations take place too which have little effect on the organisms.

However, such mutations may pass on when reproduction occurs amongst the organisms. Also, in some cases when the organism could not survive, the mutation does not pass.

Gene Flow

Let us take an example of GD in the human population assuming about a married couple in which the male is having brown eyes and the female is having green eyes.

If the green allele is dominant, even though there is a 50% chance of brown eyes too, the couple might have children with green eyes by chance. GD may take place in birds too.

We can assume a bird to have an allele for two different sizes of the beak. Now it solely depends on the alleles which show up in the offspring thereby causing genetic drift which will result in the disappearance of one of the beak sizes of the bird.

Genetic Drift not only occurs in animals but it takes place in plants too. Let us exemplify this by taking the example of a plant that produces red and yellow flowers.

Now assume that a fire broke out which destroyed the yellow flowers. Hence, the plant is then left with only red flowers and red being the dominant allele, it will result in the plant reproducing only red flowers.