The finding that human azoospermia is rescued by heterozygous PRDM9 alleles [18],[19], including some that alter DNA-binding preferences, further suggests that a reduced repertoire of satellite-DNA binding ability may be responsible for the meiotic arrest at pachytene seen not only in the hybrid mice species [15], but also in the Prdm9−/− mice [17], a possibility that directly lends itself to genetic and cytological scrutiny. The gene discussed is PRDM9; the disease is Azoospermia.