Synthetic Viability is a type of interaction between two genes, and it occurs when disruption of one gene reduces the negative effects associated with disruption of another gene
. In this example, disruption of Gene B causes lethality (cell death) because that particular gene is essential for life. However mutations in a second gene (Gene A , in the example) rescue this lethality, producing “synthetic viability“. If phenotypes other than lethality are suppressed, this is also known as “synthetic rescue“.
This type of genetic interaction is particularly useful to study gene function because it gives us tools to uncover the “backup circuits” present in every cell. If lethality caused by loss of gene B does not occur in normal conditions, but only in the presence of drugs, synthetic viability becomes a powerful tool to identify the target of the drug and investigate the mechanism the drug uses to kill cells. It also allows to understand how backup genetic circuits promote drug resistance.