A single cyclin A gene has been identified in Drosophila while Xenopus, mice and humans contain two distinct types of cyclin A: A1, the embryonic-specific form, and A2, the somatic form. Cyclin A1 is prevalently expressed during meiosis and early on in embryogenesis.
In the context of cell cycle regulation, a single cyclin A gene has been found in Drosophila, whereas other organisms like Xenopus, mice, and humans have two distinct forms: A1, primarily active during embryonic development, and A2, more commonly expressed in adult tissues. Cyclin A1 is mainly expressed during meiotic processes and early stages of development.