genetic screen
A genetic screen is a systematic hunt through many mutated organisms to find the rare ones in which a particular process has gone wrong, thereby fishing out the genes that control that process. It is like testing thousands of light bulbs to find the few that flicker, then opening those up to learn what part is broken.
A typical screen begins by inducing mutations across a large population, then applying a clear test — the assay — that distinguishes individuals with the trait of interest from the rest. Animals or cells failing the test point to genes essential for the process; by examining enough mutants, researchers can assemble a near-complete parts list of the genes involved.
Screens can be designed to be saturating, meaning large enough that nearly every relevant gene is hit at least once, and they can probe almost anything testable: development, behaviour, drug resistance or a cell's response to stress. The price is scale and a well-chosen assay, since a screen is only as good as its ability to spot the phenotype it seeks.
In a landmark fly screen, researchers examined tens of thousands of mutant embryos and sorted them by which part of the body pattern was disrupted, mapping out the entire genetic program for building a segmented body.
Sifting many mutants to assemble a complete parts list of genes.
Screens come in two flavours: forward screens (mutate at random, then find the phenotype) and targeted screens such as CRISPR screens that knock out known genes one by one across a library.