Although the amount of H2AX, as well as the percentage of H2AX in respect to the total H2A of the histone family is not the same between differentiated cell types, the percentage of chromatin that becomes phosphorylated per one DSB has a roughly constant average. That permits the quantification of the γH2AX foci  in cell lines, primary cells, and tissues. Assays based on specific antibodies against the characteristic γH2AX epitope (e.g., confocal and epifluorescent microscopy, flow cytometry, ELISA, immunoprecipitation etc.) have been incomparably successful for the detection of DSBs . Among them, immunocytochemical detection of γH2AX has become the primary method of detection, as it is several orders of magnitude more sensitive than other methods and has the potential for quantification . In addition, it has been shown that γH2AX foci are formed preferentially in euchromatin after IR-exposure .