One of the most intrinsic features of γH2AX is that γ-phosphorylation extents at megabase-long domains in chromatin. The γ-phosphorylation of H2AX is evident within minutes after the generation of DSBs. Nevertheless, γ-phosphorylation is not restricted to the vicinity of the sites of the DSB, but extends both sides of the damage, and reaches megabase-long domains in chromatin . This feature of γ-phosphorylation is very important; it represents a biological amplification mechanism where one DSB induces the γ-phosphorylation of thousands of H2AX molecules along megabase-long domains of chromatin that are adjusted to the sites of DSBs. The γ-phosphorylated megabase-long chromatin domains that are adjusted to the sites of one DSB are the basis for a very important technological implication. As one DSB is surrounded by thousands of γ-phosphorylated H2AX nucleosomes, specific antibodies enable the microscopy observation of the site of one DSB by immunocytochemistry. When detected with epifluorescence or confocal microscopy, γH2AX foci appear as large, roughly spherical conformations in cells that are in the G0, G1, S, or G2 phase of the cell cycle .