It seems that unlike Megadrive pads, the Genesis ones have a select
Both pads are identical, Megadrive/Genesis pads/machines/games are just the same apart from the name and the power supply,
Apart from the not so clever Japs who thought by making the carts slightly wider they would restrict them to Asia countries only, easy to bypass just file down both sides slightly of the MD/Genesis cart slot.
Same as the Snes/Famicon