<p>
</p>
<p>… or even in the same department. Some profs hold multiple appointments, so all you have to do is get formally admitted into one of the departments of which a guy who holds a joint appointment is affiliated. </p>
<p>I’ll give you an example from Berkeley. I know a girl who got her BS in chemical engineering from Berkeley, doing research under Jay Keasling, arguably the pre-eminent biochemical engineering researcher in the world today (was named Discover Magazine’s Scientist of the Year 2006). Berkeley ChemE has an anti-incest rule that forbids former undergrads from entering their PhD program. {Note, this rule is not unusual - lots of departments at lots of schools have similar rules. The idea is that the department doesn’t want its students to become ‘ingrown’ and stagnancy, so they want them to go out and become exposed to different profs and different ideas.} So she couldn’t apply back to the ChemE department. </p>
<p>So what did she do? She just applied to the Berkeley Bioengineering department, a department that Keasling holds a joint appointment in. She got in, and ended up going right back to the Keasling lab, and going right back to extending the research that she had been doing as an undergrad. So she was basically able to sidestep the anti-incest rule by ‘technically’ getting her PhD from another department, when, really, she ended up right back in the same lab, under the same prof, and doing the same research that she had always been doing. The whole point of an anti-incest rule in the first place is to prevent ‘ingrowth’ and stagnancy by forcing you to see new things, yet this girl went right back to doing exactly the same thing she had always been doing. A lot of people were asking why should the department even have an anti-incest rule if she is allowed to pull off something like that.</p>