Genetic screen

A genetic screen or mutagenesis screen is an experimental technique used to identify and select individuals who possess a phenotype of interest in a mutagenized population. Hence a genetic screen is a type of phenotypic screen. Genetic screens can provide important information on gene function as well as the molecular events that underlie a biological process or pathway. While genome projects have identified an extensive inventory of genes in many different organisms, genetic screens can provide valuable insight as to how those genes function. Forward genetics (or a forward genetic screen) starts with a phenotype and then attempts to identify the causative mutation and thus gene(s) responsible for the phenotype. For instance, the famous screen by Christiane Nüsslein-Volhard and Eric Wieschaus mutagenized fruit flies and then set out to find the genes causing the observed mutant phenotypes. Successful forward genetic screens often require a defined genetic background and a simple experimental procedure. That is, when multiple individuals are mutagenized they should be genetically identical so that their wild-type phenotype is identical too and mutant phenotypes are easier to identify. A simple screening method allows for a larger number of individuals to be screened, thereby increasing the probability of generating and identifying mutants of interest. Since natural allelic mutations are rare prior to screening geneticists often mutagenize a population of individuals by exposing them to a known mutagen, such as a chemical or radiation, thereby generating a much higher frequency of chromosomal mutations. In some organisms mutagens are used to perform saturation screens, that is, a screen used to uncover all genes involved in a particular phenotype. Christiane Nüsslein-Volhard and Eric Wieschaus were the first individuals to perform this type of screening procedure in animals. Reverse genetics (or a reverse genetic screen), starts with a known gene and assays the effect of its disruption by analyzing the resultant phenotypes.