Radiation Hybrid Mapping
Usually 100 - 120 clones.
Use PCR to see if genes are in certain clones.
Assumption is that the closer the genes the more likely they are in the same fragment.
Distances are presented in Ray (R) units. These distances are converted to cR units on the RH map. Linkage groups, or single unlinked markers, are ordered according to marker position on the genetic map.