DNA double-strand breaks (DSBs) induced by ionizing radiation cause the phosphorylation of histone H2AX at serine 139, forming γ-H2AX. This modification is detected as discrete nuclear foci within minutes of radiation exposure, with numbers comparable to the number of DSBs. γ-H2AX foci are observed in various species, including mammals, Xenopus, Drosophila, and yeast, indicating a conserved response to DSBs. These foci form at sites of DSBs and persist for several minutes, decreasing over time as DSBs are repaired. In mitotic cells, γ-H2AX foci appear on chromosomes, suggesting their role in monitoring chromosomal integrity. The formation of γ-H2AX is rapid, with maximal levels reached within 10 minutes, and is associated with DNA repair mechanisms such as nonhomologous end-joining and homologous recombination. γ-H2AX foci are also detected in laser-induced DSBs, confirming their role in identifying and responding to DSBs. The presence of γ-H2AX foci correlates with the number of DSBs, indicating that each focus represents a DSB. These findings highlight the importance of γ-H2AX in the detection and repair of DSBs, and its conservation across species. The study also reveals that γ-H2AX forms in response to DSBs in both interphase and mitotic cells, and that its distribution reflects the chromosomal location of DSBs. The results suggest that γ-H2AX plays a critical role in the cellular response to DSBs, and its formation is a universal response to DNA damage.DNA double-strand breaks (DSBs) induced by ionizing radiation cause the phosphorylation of histone H2AX at serine 139, forming γ-H2AX. This modification is detected as discrete nuclear foci within minutes of radiation exposure, with numbers comparable to the number of DSBs. γ-H2AX foci are observed in various species, including mammals, Xenopus, Drosophila, and yeast, indicating a conserved response to DSBs. These foci form at sites of DSBs and persist for several minutes, decreasing over time as DSBs are repaired. In mitotic cells, γ-H2AX foci appear on chromosomes, suggesting their role in monitoring chromosomal integrity. The formation of γ-H2AX is rapid, with maximal levels reached within 10 minutes, and is associated with DNA repair mechanisms such as nonhomologous end-joining and homologous recombination. γ-H2AX foci are also detected in laser-induced DSBs, confirming their role in identifying and responding to DSBs. The presence of γ-H2AX foci correlates with the number of DSBs, indicating that each focus represents a DSB. These findings highlight the importance of γ-H2AX in the detection and repair of DSBs, and its conservation across species. The study also reveals that γ-H2AX forms in response to DSBs in both interphase and mitotic cells, and that its distribution reflects the chromosomal location of DSBs. The results suggest that γ-H2AX plays a critical role in the cellular response to DSBs, and its formation is a universal response to DNA damage.