What Is Genetic Drift

Also known as allelic drift, genetic drift is described as an evolutionary mechanism occurring by chance randomly and not by natural selection. The frequency in a specific allele changes in the population just by chance and is not influenced by any adaptation need. It is different from natural selection which is a survivalist adaptation, where the frequency of the allele is changed so as to be fit to reproduce and survive. In comparison to natural selection, genetic drift covers a small population where as natural selection affects a large population.

Understanding alleles

  • The genetic variant, the factor responsible for specific traits in an organism is called an allele. It is expressed as dominant and recessive where the dominants allele gets to be expressed in the offspring.
  • The two parents donate alleles of a trait to form a gene in the offspring, the dominant one is what will be shown for example skin color or height of the offspring.
  • In a population of mixed black and white people as an example, in tropical climates, white people are more susceptible to skin cancer and die faster than their black skinned counterparts. A case like this will ensure the black allele is dominant and reproduction will make this allele be expressed more in the population. When this happens, the frequency of the black allele will increase. More white people will die before passing on their white skin gene. This example describes natural selection where a factor in the environment determines the allelic frequency.
  • An illustration of genetic drift will be a random case where, half the population of white people are hit by lightning and die with the remaining half succumbing to malaria. The population will have more black alleles being passed on to off springs hence a high allelic frequency. This random occurrence can then be described as genetic drift.

It just happens by chance that a specific trait is passed on more to descendants than others. Anything that causes some organism with a given trait to leave more off springs in the population will cause a genetic drift.  A sampling error is another cause of allelic drift, a skewed sample chosen for a study will give a drift in gene depending on what the sample consist of.

The drift will become fixed at the time when no more of a given trait is expressed at all in a population. This will ensure that all future off springs will have only the chance dominant traits, not because of any need to survive, but only by luck.


Genetic drift takes effect more rapidly in smaller populations, in a population bottleneck where a sudden drop in population size occurs may be due to a catastrophe, the drift will work quickly. It also becomes effective in founder effect where a small part of the population is isolated to reproduce in segregation.