"A unit of genetic map distance defined corresponding to an interval in which there is a 1% probability of X-irradiation induced breakage. To be completely specified, the unit must be qualified by the radiation in dosage in rads (e.g. cR8000), because this determines the actual breakage probability." [NCBI:http\://www.ncbi.nlm.nih.gov/SCIENCE96/Glossary.html]