Definition : Genetic interactions between genes occur when two genetic perturbations (e.g. mutations) have a combined phenotypic effect not caused by either perturbation alone. A gene participant in a genetic interaction represents the gene that is perturbed. Genetic interactions are not physical interactions but logical (AND) relationships. Their physical manifestations can be complex and span an arbitarily long duration. Rationale: Currently, BioPAX provides a simple definition that can capture most genetic interactions described in the literature. In the future, if required, the definition can be extended to capture other logical relationships and different, participant specific phenotypes. Example: A synthetic lethal interaction occurs when cell growth is possible without either gene A OR B, but not without both gene A AND B. If you knock out A and B together, the cell will die.
Source:http://www.biopax.org/release/biopax-level3.owl#GeneticInteraction