[1] Radiation hybrid mapping consists of several steps.
[2]: 82 Radiation hybrids are generated by using X-rays to randomly break chromosomes into fragments, then implanting the fragments into non-irradiated rodent cells, which replicate and thus clone the chromosomes.
If two given DNA markers are far apart on the initial chromosome, then it is likely that they will appear in distinct fragments.
The frequency of the separation of the markers into different fragments is used to estimate the chromosomal distance between them.
For example, the RH procedure was used to map 14 DNA probes from a region of human chromosome 21 spanning 20 megabase pairs.