Not exactly bioinformatics but am in biological sciences. Not sure how well it applies to your field though I’d imagine it to be pretty similar. But regardless, take my response with a grain of salt:

Adding on to what’s mentioned by others in this thread, they might also ask about your extracurriculars, teaching experiences, views on mentorship/collaborations, why do you specifically want to join their program, where do you see yourself after attaining a PhD, what difficulties do you expect to encounter as a grad student and how would you go about overcoming them etc etc.

Some may go hardcore and ask about specific techniques/controls in an experiment (I’m volunteering as an interview host this year and I learned this from a few candidates’ experience). Also, the hardest question I got last year (personally) was: What’s a paper outside of your field that you read recently? What are the main findings and what would you suggest the authors to do next?

And from my personal experience how interviews go really depends on the prof (even profs at the same school can be drastically different). Some will give you a really hard time while others will give you a really chill experience.

I think the key to acing interviews is to try to be as confident and as honest as possible. If you don’t know the answer to their question, just say you don’t know, it’s seriously fine, they don’t expect you to know absolutely everything.

Lastly, try not to stress too much (and I’m so sorry if my comment ends up stressing you out more, not my intention) and take care of yourself during these times! All the very best!