they say all the subjects are equally distributed and i bet they're, when taking into account all the exams given around the world. However an individual exam can be skewed towards one subject over another, i had a lot of path, pathophys, and phys. almost no anatomy or pharm. Someone told me his exam was mostly anatomy and histology. I would say the high yeild subjects will be ethics, biostat, path, pathophys, pharm, micro, then clinical anatomy like dermatomes and bracheal plexus.
But in reality they can ask you anything and everything and they do. They asked me some obscure genetics q's on mine but there weren't too many of those. first aid for step1 has a good overfew of what you need to know but u'll need to add some detail to it.