What is the generally accepted Reformed position on how original sin is transmitted?

Just what the title says. How, in the Reformed tradition, is the transmission of original sin understood to occur? Following on the heels of that question, what is the biblical/theological justification to that?

My understanding is that Federal Headship is the explanation favored among the reformed, but I confess that I have not explored this in great depth. What are common objections heard to this position, and how are they responded to?