reverse genetics
Reverse genetics runs the detective story backwards. Instead of starting with a puzzling trait and hunting for the gene, you start with a known gene whose function you want to learn, deliberately change or switch it off, and watch what goes wrong. The disturbed organism tells you what that gene was normally doing.
Common tactics include knocking a gene out entirely, dialing its activity up or down, or silencing the message it produces. Modern genome-editing tools let researchers target a chosen gene with precision, so that almost any gene revealed by genome sequencing can be tested directly for its role in development, physiology or disease.
Reverse genetics became essential once whole genomes were sequenced, because sequencing reveals thousands of genes whose jobs are unknown. Its main caution is that knocking out a gene may produce no visible effect — perhaps because another gene compensates — so a silent result does not always mean the gene is unimportant.
Curious about a newly sequenced gene of unknown function, a team uses CRISPR to disable it in mice and discovers that the animals develop abnormal hearts — pinning a role on the gene.
From a known gene to its hidden job, by breaking it on purpose.
Knockout mice, gene silencing by RNA interference, and CRISPR editing are all reverse-genetics tools: each starts from a chosen gene and asks what its loss or change does.