What is the biblical basis for the doctrine of original sin?

I was recently discussing theology and baptism with my Arminian teacher when he mentioned that he doesn't believe in the doctrine of original sin, saying "I don't believe sin is genetic". This actually caught me off guard, as I was unaware that there even was a dispute over the doctrine of original sin. Yet later in the day and in the next following days, I spent a little bit of time looking for the basis of such a doctrine. I wasn't really able to find anything online. So that leads me to my question. What is the biblical basis for the doctrine of original sin? It may be helpful to me if you defined what is meant by original sin, as I may just be confused.