In the United States, a professional interview is subject to basic legal rules. Specifically, admissions officers and residency directors should refrain from asking interview questions that are not relevant to the position the interviewee is seeking. Questions about race, religion, sexual orientation, and marital or family status fall into this category.
If you are asked these types of questions, you can respond by addressing the intent of the question without revealing personal information. (“I think you’re asking if my home life will affect my ability to carry out my medical school studies or my clinical duties. I can assure you it won’t, and I’ll complete my full tenure here at your school.”)
If you have the opportunity to give feedback to the institution about your interview questions or experience, you can consider doing so after the interview. When I was interviewing for residency, I was asked by a faculty member if I had a boyfriend. After the interview day, I talked to a faculty mentor at my school who reported the situation to the other institution. The faculty member who asked me the illegal question was no longer permitted to interview.