Question about alternates

I'm not a premed, I am hoping to go to graduate school, but I have a question that some premeds probably have. I applied to a research program at a local biomedical graduate school that is part of a medicial school. I wasn't accepted, but I was put on the alternate list. I have no idea what my chances are of ending up getting in. What have been people's experience with being alternates? How often do alternates get into the program they apply to? Do schools usually have a list of alternates terribly longer than the amount of seats they expect to open?