Cyclin A1 is a member of the highly conserved cyclin family that is characterized by a dramatic periodicity in protein abundance, and belongs to the A-type cyclin subfamily. The mammalian A-type cyclin family consists of two members: cyclin A1 and cyclin A2. Different cyclins exhibit distinct expression. Cyclin A1 is expressed in mice exclusively in the germ cell lineage and high rate of cyclinA1 is found in human testis and certain myeloid leukaemia cells. Cyclin A1 is primarily function in the control of meiosis. It serves as regulator subunits binding to cyclin-dependent kinase 1 (Cdk1) and cyclin-dependent kinase 2 (Cdk2), which give two different kinase activities, one appearing in S phase, the other in G2. Through this, cyclin A1 operate the entry and progression in cell cycle. High frequency of cyclin A1 overexpression has been observed in acute myelocytic leukemias, especially those that are at the promyelocyte and myeloblast stages of development.