Gene redundancy is the existence of several genes in the genome of an organism that perform the same role to some extent. This is the case for many sets of paralogous genes. When an individual gene in such a set is disrupted by mutation or targeted knockout

Gene knockout

A gene knockout is a genetic technique in which one of an organism's genes is made inoperative . Also known as knockout organisms or simply knockouts, they are used in learning about a gene that has been sequenced, but which has an unknown or incompletely known function...

, there can be little effect on phenotype

Phenotype

A phenotype is an organism's observable characteristics or traits: such as its morphology, development, biochemical or physiological properties, behavior, and products of behavior...

as a result of gene redundancy, whereas the effect is large for double or triple gene knockouts.