I’m talking about present Jewish law, for which marital status of the mother is not particularly relevant. Jewish law has diverged in quite a number of ways from what says in the Torah.
http://en.wikipedia.org/wiki/Who_is_a_Jew%3F#Jewish_by_birth
I’ve been led to believe that status of Jew passes from the mother, as Jewish women were so often sold into sex slavery, that the conquering slave-taker could not confer his religion onto the progeny.