H2AX and severe combined immunodeficiency: To this end, we quantified γ-H2AX foci present associated with chromatin remodeling and determined the kinetics of γ-H2AX foci formation and disappearance (repair) after γ irradiation, by studying elongated spermatids present in meiotic spread preparations from Rad54/Rad54B double knockout (dko) mice, DNA-PKcs deficient Severe Combined Immunodeficiency (SCID) mice, PARP1-inhibitor treated mice and their appropriate wild types.