Genetic screen

In a genetic screen, certain phenotypes are selected in a mutagenized population to unravel the function of a specific gene in a biological pathway.

There are two different types of screens: forward and reverse genetic screens. In a forward genetic screen, genes are identified based on a known phenotype, whereas in a reverse genetic screen, the phenotype is analyzed based on known genes.

Forward genetic screen

Random mutations are introduced into the organisms of interest by subjecting them to a mutagen (i.e EMS). The offspring is then screened for the desired phenotype.

If the mutation is recessive, a complementation test is performed to rule out the possibility of multiple mutations causing the phenotype: If the offspring of the recessive mutants is wildtype, it is assumed that the phenotype is determined by more than one gene. In this case, or if the mutant doesn't produce viable offspring, a different mutant from the parental generation is chosen.

Finally, the genome of a mutant is sequenced and analyzed to find the potential mutation causing the observed phenotype. For confirmation, a copy of the intact gene is injected into a mutant to rescue its progeny.