Question

When natural selection acts to eliminate the extreme phenotypes and favours the intermediate phenotypes in a population, it is termed as-

• A. Disruptive selection
• B. Directional selection
• C. Stabilising selection
• D. Diversifying selection

Answer 1

The correct option is C Stabilising selection

Natural selection is a process in which organisms that have inheritable variations which enable better survival reproduce and leave a greater number of progeny.

There are three types of natural selection
a. Stabilising selection: When natural selection operates in such a way that individuals with mean (average) value of the trait are favoured,it is called stabilising selection.
Hence, stabilising selection acts to eliminate extreme phenotypes and favour individuals with intermediate phenotypes. This leads to the multiplication of intermediate phenotypes. This mode of selection reduces variation and tends to maintain a particular phenotypic character.

b. Directional selection: When natural selection operates in such a way that individuals with extreme value of the trait are favoured thereby shifting the curve for the phenotypic character in that direction, it is called directional selection. Directional selection operates in response to gradual changes in the environmental conditions.

c. Disruptive selection/Diversifying selection: When natural selection operates in such a way that individuals at both the extreme values of the trait are favoured and individuals with mean value of the trait are eliminated, it is called disruptive selection. Consequently, the original population is disrupted into two or more separate groups, that later evolve into new species.

Hence, stabilising selection acts to remove the extreme phenotypes from a population, as a result of this, the frequency of the intermediate phenotypes increases.