I think it was VPI that posted about being able to distinguish between genetic identical twins from one fertilized egg that split and fraternal twins from two fertilized eggs that just happened to get shelled together by looking at how they connect to the yolk. I've only had one set of twins so far (in my very first ball python clutch back in 2000). They where both male so could have been the identical type but I have no idea how they connected to the yolk. If you get a male female twin pair you would know they where two eggs shelled together but the same sex could be shelled together just by chance. I think the exact pattern would be like a fingerprint with some details determined by chance which explains whey genetically identical twin humans have different fingerprints.