If I'm doing an MS before applying to (top 20) US PhD programs, is there any particular expectation to be deeper in a specialization than if I had applied straight from undergrad? The issue is that I'm doing my MS at the same institute where I did my undergrad, and they will not let me retake the grad classes I took as an undergrad, which includes nearly all the courses relevant to my intended area of specialization. In the past year, I was so busy with completing my remaining major requirements (not to mention quite depressed) that I've forgotten almost everything I learned in those courses, and there was one particular sequence of courses in which I never really understood the material to begin with. I definitely won't be able to review all of this material on top of my full graduate courseload, but I've also sort of started gravitating toward other areas anyway. But the problem there is that I won't be able to learn any of those deeply enough in one year to lay out a precise set of research interests for my PhD application.