Genetic Screens

Genetic screens are analytical tools for studying the correlation between the genotype and the phenotype of an organism. They are broadly classified into forward genetic screens and reverse genetic screens.

Forward screens involve identifying the genes responsible for an observed characteristic, such as petal color, thus using a known phenotype to study an unknown genotype.

These screens usually involve the genome of an organism being randomly mutated to induce a change in phenotype. Next, the mutant organisms are bred until genes are homozygous, to ensure expression of recessive phenotypes. Organisms are then screened for traits of interest.

For example, to identify genes responsible for morphological defects in zebrafish embryos, sperm cells of adult males are mutated with a chemical, ethylnitrosourea, and then crossed with a wild type female.

The resulting F1 males are crossed again with a wild type female and dominant mutations observed in the F2 progeny. F2 individuals are then inbred to identify recessive gene mutants in F3 individuals.   

Genes responsible for the altered phenotype can then be determined by different methods. In one technique, genomes of multiple mutant and