My understanding is that it depends on the circumstances. A person of Jewish lineage who becomes Christian for a reason other than duress isn't Jewish. They are two distinct religions, with actually very little in common.
A Christian is a broad term it really is not a religion. It means one thing and one thing only that you believe Jesus is the Son Of GOD and the saviour of the world.
Religions are Baptist, Lutheran Jehovah Witness..
Just in case you didn't know...