A genetic interaction in which a combination of mutations in two or more genes of a single strain results in a phenotype that is different in degree or nature from the phenotypes conferred by the individual mutations. The most common type of synthetic interaction is synthetic lethality, in which two mutations, neither of which causes inviability when present individually, cause inviability when present together in the same strain. Synthetic interactions may result in other phenotypes, e.g., slow growth or respiratory growth defect. Synthetic interaction can be an indication that the genes involved participate in the same pathway or process; synthetic interaction between two point mutant alleles may be an indication that the gene products physically interact.

This definition is in context to Yeast Genome. See more contextual defintions for Synthetic Genetic Interaction.