Between Years 1 & 2:
Most programs have specific requirements for advancement to the second year of graduate study, usually related to satisfactory academic performance and mentor selection. Many programs will require that you maintain a minimum graduate GPA of 3.0 or better. Some programs have comprehensive written exams at the end of the first year that must be passed before advancement to the second year. Some programs may require that you have successfully declared a mentor before proceeding to the second year, and your funding may be linked to your mentor selection (see also Financing Your Graduate Education).
Between Years 2 & 3:
Admission to candidacy for the PhD degree usually involves a qualifying exam, for which the format varies across institutions. Some qualifying exams include comprehensive written examinations covering key concepts from coursework and/or other competencies that are part of the curriculum. Some programs require a written research proposal, sometimes in the format of an NIH grant proposal, which may be written on your own research topic or something unrelated to your own research. Most qualifying exams include an oral component administered by a group of faculty members, usually including your thesis committee. Again, the format varies from program to program, but usually includes open-ended questions designed to probe the depth of your background knowledge and understanding of key scientific principles related to your research project. The oral examination may also assess your skills at hypothesis generation, experimental design, data interpretation, ability to anticipate experimental pitfalls, and troubleshooting.
Around Years 4-5:
Many programs require a "pre-defense" meeting with your Thesis Committee six months to a year before your planned graduation. The purpose of this meeting will be to review your progress toward completing your specific aims, review an outline of your dissertation, and establish a timeline for completion of experiments and writing your dissertation. Some students continue doing experiments until the very end, but at some point you and your mentor and committee must agree to what experiments are to be included in your dissertation and which (final) experiments will not be in the dissertation. It is also useful to review the status of your publications at this time (see also Presenting Your Research).
Years 5 and Beyond:
Time-to-degree is variable between and within graduate programs, and depends on many factors, such as how hard you work, your experimental design, how long it takes to generate key reagents, cell lines, mouse strains, etc., and sometimes how lucky you are. Your dissertation defense will consist of submission of a written dissertation according to the guidelines of your institution, a public seminar about your research, and an oral examination by your committee members. The oral exam may test your background knowledge, approaches used to answer your question, integration of your results with the broader field, and ability to pose questions for future research.