A gene knockdown is either a genetically modified organism that carries one or more genes in its chromosomes that has been made less active or had its "expression" reduced or is the use of a reagent such as a short DNA or RNA (oligonucleotide) with sequence complementary to an active gene or its mRNA transcript. This oligonucleotide will bind to this active gene (or its transcripts) to decrease expression of a specific gene, copying the effects of such a genetic modification. So far such organisms have been engineered chiefly for research purposes. Also known as knockdown organisms or simply knockdowns, their most direct use is for learning about a gene that has been sequenced, but has an unknown or incompletely known function, an experimental approach known as reverse genetics. Researchers draw inferences from how the knockdown differs from individuals in which the gene of interest has not been made inoperative. Knockdown includes the processes of modifying an organism (as described above) or of using a reagent to suppress gene expression, as in "knocking down a gene."