My undergrad was a mess for various personal reasons, namely revolving around my wife's chronic illness, which pulled me out of school for weeks at a time. Also, I made up for it with over a year's experience working at a hospital, and my strong MCAT. The MCAT is not an obstacle. It's a tool- really the only one you've got- to help show them you've improved.
Sgu never asked me to explain. But I took the initiative and explained it anyway in my essay to them. I told them the truth: my wife's illness turned my interest in medicine into a passion.