Very standardized process. Every week they interview about 30-40 students and organize events for them on a two-day schedule. The interviews take place on the second day (first day they show them around the med center, and have a nice dinner planned with actual grad students and professors). Each applicant is assigned to 3 PIs who he/she will talk to for about 30 minutes each. In my case one of them had an emergency so it was only two. On the written application you can actually put a couple PI names that you would like to talk to as part of your interview process but it does not guarantee anything. Depending on the PI, your interview will be a chat about yourself, your previous research experience, why you are applying to grad school, and then you should ask about their research. If you're clever, you have read one of their papers already and that will impress them. The interviews are really laid back, in the end it really feels like a conversation about science and research. Some PIs may have an exercise to test your analytical mind, but I haven't experienced it.

The interviewing process was very intense but nothing that any one wanting to be in the field of bio medical research could not handle. The three professors that I interviewed with all expected me to know the research that I had completed in undergrad but they were not mean or unfair in their expectations at all. Just know your research and be personable and you should be fine.