There is an adapter for the Cyber Gadget Retro Freak emulator console that allows you to play SG-1000, Mark III, and Game Gear games. It's called the Gear Converter. I came across this video review about it. In it, the reviewer mentions that the Gear Converter fits in the actual Sega Mega Drive and works with Mark III cartridge and card games. Yes, the adapter will allow you to play Mark III games on the Mega Drive. Unfortunately, Game Gear games don't work. I asked him if SG-1000 games will also work in the adapter on the Mega Drive, but he told me that he didn't have any games to test. I'm thinking of picking up this adapter for my Mega Drive. I've had my eye on Alex Kidd BMX for awhile and if the adapter will save me the bother of hunting down a Mark III console and finding space for it, I'm sold. But I am curious if it will also make the Mega Drive compatible with SG-1000 games. There are a few SG-1000 games I'm interested in, but not enough to hunt down an obscure console that only supports RF. Does anyone know if this adapter works with SG-1000 games on the Mega Drive? Thanks.
Apparently not. http://www.smspower.org/forums/13446-MasterEverdriveDoSG1000RomsWorkOnAMegadrive A master system can play them, although the colours are supposedly not correct.