ATR and infertility disorder: In contrast, a mouse model expressing kinase-dead ATR (ATR+/KD) but not ATR loss (ATR−/−) exhibited ssDNA-dependent defects at the non-homologous region of X–Y chromosomes during male meiosis, resulting in sterility, and at telomeres, rDNA, and fragile sites during mitosis, resulting in lymphocytopenia [29].