Non-self recognition during asexual growth in filamentous fungi is mediated by interactions between proteins encoded by heterokaryon incompatibility (het) genes. For example, N. crassa strains that carry the incompatible factors un-24PA and het-6OR exhibit a slow and aberrant growth phenotype. Remarkably, after about 4.5 days of growth, wild-type-like sectors emerge from these self-incompatible un-24PA het-6OR colonies through a process called ‘escape’. Escape is due to point mutations that arise in het-6 gene (94%), vib-1 (3%), a transcription factor of het-6, or other factor(s) (3%) that have only been characterized by a unique feathery morphology. Results show that deletions of the DNA damage checkpoint factors, mus-9, uvs-3, mus-23, vib-1 and rtt109 either suppress or delay escape from incompatibility. We proposed that het-6 and vib-1 are DNA damage checkpoint effectors.