A radiation hybrid can also be used as a mapping reagent in STS mapping which refers to a hamster cell line carrying a relatively small DNA fragment from the genome of a second organism (such as human). For example, formation of radiation hybrid between human cell and hamster cellas shown in Figure 6-5.3(b).3.3 . After fusion of the two cells, the presence of markers in human DNA within the hybrid cell line is analyzed by hybridization or PCR methods. Same radiation hybrid will result if the two markers are close together thereby having greater probability to be on the same DNA fragment.

Figure 6-5.3(b).3.3: Radiation hybrids(a) Irradiation of human cells: formation of smaller fragments by low X-ray doses and larger fragments by higher doses (b) Formation of a radiation hybrid by fusion between an irradiated human cell and an untreated hamster cell.

(Source: Brown TA. 2002. Genomes. 2 ^nd ed. Oxford: Wiley-Liss )