Genetic mapping based on radiation hybrid data.

Radiation hybrid mapping is a recently developed technique for constructing high-resolution maps of mammalian chromosomes. The chromosome of interest is exposed to X rays, which cause it to break into numerous fragments. The fragments are randomly recovered into hamster cells. The resulting hybrids are then analyzed for the presence or absence of DNA markers of interest. A simple method for using this information to order the markers on the chromosome is developed here. For any particular ordering of the loci, the least number of breaks consistent with the data can be determined. The best order is taken to be that which minimizes this number of obligatory breaks. Some statistical properties of the method are examined, both theoretically and by use of a simulation study. Except for some extreme cases, the method gives good results, which compare well with results obtained by a full maximum likelihood analysis. The method is used to order a set of 14 loci on chromosome 21 with encouraging results.