Genetic Variation
Genetic variation refers to the variation in the genome sequences between individual organisms of a species. Individual differences or population differences can both be referred to as genetic variations. It is primarily caused by mutation, but other factors such as genetic drift and sexual reproduction also play a major role.
Quantitative Genetics
Quantitative genetics is the part of genetics that deals with the continuous trait, where the expression of various genes influences the phenotypes. Thus genes are expressed together to produce a trait with continuous variability. This is unlike the classical traits or qualitative traits, where each trait is controlled by the expression of a single or very few genes to produce a discontinuous variation.
What is Genetic Drift? and what is its significance?
The basic purpose of evolution is to change the existing population into a new and better form of population and for that reason, it results in changing the allelic makeup of the population by the process of natural selection. On the other hand, this change in the allele frequencies can also occur by the process of genetic drift. Both natural selection and genetic drift function with the same aim to change the allelic frequencies of the population but with two very different approaches.
Genetic drift is a change in allelic frequencies of the population by random change simply as a result of chance or sampling error whereas natural selection works on the basis of better-fit character. Genetic drift is a non-adaptive and non-directional mode of evolution that occurs in almost all populations but more evident and profound in small-sized populations.
For example,
Let us consider a small population size of 20 individuals in which 10 individuals are having green eye color governed by allele A and 10 individuals are having blue eye color governed by allele a. Now, if any natural catastrophe like cyclone fires and 50% of the individuals died and all the lost individuals were with green eyes then it would result in the fixation of blue eye colored individuals in that area because they are the only ones who survived.
Here we can clearly see that by chance there is no change in the allelic frequencies of A but a huge change in the allelic frequencies of the allele a which means genetic drift can derive each allele to either fixation or loss. Once an allele becomes fixed, genetic drift comes to a halt and the overall population becomes very different from the previous population. This is purely chance-based and with this, any beneficial allele can be lost or any harmful allele can be fixed in a population.
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