Radiation hybrid mapping.

A theory is developed to predict marker retention and conditional retention or loss in radiation hybrids. Applied to multiple pairwise analysis of a human chromosome 21 data set, this theory fits much better than proposed alternatives and gives a physical map consistent with other evidence and robust with respect to errors to typing. Radiation hybrids have great promise to provide order and physical location at two levels of resolution, spanning the techniques of linkage and restriction fragments and not limited to polymorphic loci.