Most places want the GRE, but not everyone weighs it the same. Most places want upper division courses in the following areas: Gen chem 1 and 2, Organic Chem 1 and 2, Biochem, and Anat and Phys. But each program is different, and may require things like abnormal psychology, biology, calculus... the list goes on. The only useful answer anyone can give is for you to look at the prereqs on the websites of the schools you are interested in, because it all varies to some degree. Some don't have strict math requirements, but others do. Its the same for so many courses.