Question

Explain what is Genetic drift and discuss some examples of genetic drift affect human population

Answer 1

Here are some examples of genetic drift affect human population

Example 1:

Let us think of a case of a population of 100 individuals which is a very small population, of whom 95are of 'O' blood group and the rest of them are of 'B' blood group. Because of several factors like accident, illness, non availability of mating partners the individuals of B blood group may be  gradually eliminated. Thus in this process, increase or decrease of of a particular allele does not depend upon advantageous or disadvantageous conditions, but that happens merely as an accident or chance. Therefore, this is referred to as chance fluctuation or accidental loss or fixation of gene.

Example 2:

Suppose there was  a small population of brown-eyed individuals, a few members of which were blue-eyed. By chance these blue-eyed individuals migrated to some other place or locality and settled there in isolation to give rise to another small population of blue-eyed. From the parental population, blue-eye was lost accidentally, whereas in the new population that the gene was fixed.

Drift is important in 3 cases:

 A. It is important for removing or promoting very rare alleles, especially new favorable mutations before they become established, because drift has a greater effect than selection on the transmission of rare alleles. It is important for increasing the frequency of new recessive mutations to a frequency where homozygotes occur in sufficient frequency for selection to become effective.

B. Drift is responsible for changing the frequency of neutral mutations, which by definition are affected more by drift than selection.

C. Drift in small populations can produce unrepresentative allele frequencies which would be very unlikely to occur in a large population. This is called Founder effect, when a small and unrepresentative population founds a new colony.

                      It is also termed as Bottle necking when a population is reduced to a small number who become parents for a large later population.

                        Drift may cause small isolated populations to be a very different from the species norm, and can be important in the production of new races or species. Inbreeding can be a special case of founder effect where the effective population is small group of related individuals, possibly a single hermaphrodite individual.

Genetic Drift

• Genetic drift is the tendency within small interbreeding populations for heterozygous gene pairs to become homozygous for one allele or the other by chance rather than by selection.
• This happens to all populations.
• This is more visible and has drastic effect in small populations.
• There are 2 types of genetic drift, which includes Founder effect and Bottleneck effect.
• In addition to natural selection and mutation, the genetic drift is another factor that brings changes in the gene frequency.