The departmental website has a good overview of what a PhD entails. Here are a few more details that elaborate on a few points. To start, there are basically three ways to enter a PhD program:
You’ve got an undergraduate degree and you enter McGill at the Masters level. Here, all the rules of the Masters program apply; your thesis project will initially be given to you by your supervisor and may or may not be entirely original work. After about a year, if you decide that you like the project, the work environment and the school, you can ask your supervisor if they think you are ready to “switch up”. If your supervisor feels that the project is promising and you show the necessary skills, they will ask you to write up a thesis proposal based on your previous work but directed towards novel discoveries. Again, these ideas should be your own but advice from your supervisor can be indispensable. Then you will have your Qualifying Exam. The department secretary will help you set up your qualifying exam committee. After you pass your QE (you can!), you will need to re-apply to McGill as a new student, all the same forms as when you first arrived (and fees!). Once accepted by McGill, you will be a ‘PhD 2’ level student in the next semester and can expect to spend another 2-4 more years before submitting your thesis.
You’ve already done a Masters at another university and are coming to McGill for the first time. In this case you will still need to pass the Qualifying exam within your first 15 months. You will also need to write a thesis proposal of original research from your own ideas with guidance from your supervisor. When you enter with a Masters, expect to spend 4-6 years working before submitting.
The MD/PhD program. This is for medical students at McGill who are also interested in research. You can apply right off the bat or before Sept 1st of your second year of med school. Be warned, this is a SEVEN-YEAR program with 1.5 years of medical school classes and then 3-4 of grad studies with a thesis that you will have to defend at the end.
Note: Be aware that the department of Human Genetics has a high standard for accepting students into the PhD program. Especially since this means funding and providing space for someone for about 5 years. The current minimum GPA is 3.0 but there is talk of increasing the minimum to at least 3.2 or higher. You have better chances if you already have (or have a good chance of having) external funding when you apply. It is worth it though, once you are accepted, our department has one of the highest proportion of externally funded students and the resources are some of the best you’ll find in the country. Be prepared for some stiff competition, we are growing but still only have space/resources for about 15 (total!, Masters, PhDs, MD/PhDs and Postdocs) new students a year.