Q.What is gene "knock out" ?

Gene knockout deliberately disables a chosen gene so that researchers can study what that gene normally does, by observing what goes wrong (or changes) in its absence.

Understanding what a particular gene does is often best achieved by observing what happens when that gene is removed or disabled, rather than only studying it while it is functioning normally. In gene 'knock out' technology, one or both alleles of a target gene in a living organism (commonly a laboratory mouse, hence 'knockout mice', but also used in other model organisms) are specifically and precisely inactivated -- traditionally through homologous recombination, in which a modified, non-functional copy of the gene is introduced into embryonic stem cells and replaces the normal gene copy, or more recently through precise genome-editing tools such as CRISPR-Cas9, which can directly disrupt the gene's DNA sequence. The resulting knockout organism, which lacks a functional copy of that gene, is then studied to observe any resulting changes in development, physiology, behaviour or disease susce …