Read the following statements and select the correct option.

I. When certain individuals migrate out of the population, gene frequencies change in the population.

II. Stabilising, directional and disruptive selection are types of artificial selection.

III. Extreme phenotypes are favoured in the disruptive selection.

IV. Single step large mutation is called genetic drift.

The correct option is C I and III are correct

When some individuals migrate out of the population, it may alter the allelic frequency of the population. This change in allelic frequency is not significant in case of very large population whereas if the migration happens from a very small population, chances are that an allele can be lost completely from it. Hence, migrations out of the population can alter gene frequencies.

Natural selection is a process in which individuals which are fit in all aspects like physically, physiologically and reproductively get better adapted to the environment, thus increasing their survival chances and leave a greater number of progeny. The individuals who are not able to cope with the changing environment get eliminated. Nature selects the population via three ways i.e. stabilising, directional and disruptive selection.

The phenotypes which get eliminated and the ones which they favour for survival is given below

	Phenotypes favoured	Phenotypes eliminated
Stabilising	Intermediate phenotypes	Extreme phenotypes
Directional	One extreme phenotype	Rest all phenotypes eliminated
Disruptive	Extreme phenotypes	Mean value traits are eliminated

Single step large mutation is called saltation and it leads to the formation of new species according to Hugo de Vries. Random changes in the gene frequency by chance is called genetic drift.