Question

What is genetic drift ?

Answer 1

Example of genetic drift is the bottleneck effect . Which happens when the size of a population is severely reduced . Events like natural disasters can kill most of the individuals and leave behind a small population . It can cause genetic drift.

Complete answer:

Hardy-Weinberg principle : In a given population one can find out the frequency of occurrence of alleles of a gene or a locus . This frequency is supposed to remain fixed and even remain the same through generations.
There are five factors known to affect the Hardy-Weinberg equilibrium.
This is gene migration or gene flow , genetic drift , mutation , genetic recombination and natural selection.
When migration of a section of population to another place and population occurs gene frequency change in the original as well as in the new population.
There would be a gene flow if this gene migration happens multiple times.
If the gene migration occurs by chance it is called genetic drift . That means , Genetic drift is a factor which affects Hardy-Weinberg equilibrium in which gene migration occurs by chance.
Sometimes the change in the allele frequencies is so different in the New sample population that they become a different species .The original drifted population becomes founder and the effect is called founder effect.
Natural selection is a process in which heritable variation enabling better survival are enabled to reproduce and leave a greater number of progeny.

Note: Natural selection can lead to a stabilisation , directional change or disruption. Hardy-Weinberg equilibrium that means change in frequency of alleles in a population would then be interpreted as resulting in evolution.