The Twelve Tribes of Isreal - Genesis 49

So this week we looked at the twelve tribes of Israel.

These were: Reuben, Simeon, Judah, Zebulan, Isaachar, Dan, Gad, Asher, Naphtali, Benjamin, Ephraim and Manasseh.

Firstly we talked about Ephraim and Manasseh, and how Ephraim was given the firstborn even though he was the second son(Gen 48 v 8 - 20) The tribe of Ephraim became the largest of all the tribes.

It's interesting that there's slight differences in some places, concerning the tribes. The 12 sons of Israel were the original 12 tribes. Reuben lost his rights as firstborn by defiling Jacob's bed(Gen 49 v 3-4) In Reuben and Joseph's place, Joseph’s two sons, Ephraim and Manasseh, became tribes of Israel(Gen 48 v 5-6) In some other lists of the twelve tribes of Israel, Levi is not mentioned, presumably because the Levites were told to serve at the temple and therefore were not given any land of their own in Israel.
At this point we looked at Exodus 32, where we see the Levites loyalty towards God, in which they were rewarded with the spiritual service lost at that time by the firstborn of the other tribes.

We also briefly looked at the lost tribes of Israel. After Solomon's death, the Hebrew nation split into two kingdoms. The tribe of Judah, Simeon, Levi and Benjamin formed the Southern Kingdom, and the other tribes made up the Northern Kingdom of Israel. The Assyrians conquered the Northern Kingdom and sent the tribes into Exile, so what happened to these tribes? Anyone know?

At the end of class we looked at another list of the twelve tribes, in which Joseph is listed as a tribe, along with his son Manasseh. Ephraim and Dan are both missing from the list.
Every list in the Bible contains Simeon, Judah, Gad, Asher, Naphtali, Manasseh, Issachar, Zebulun, and Benjamin. To add to those nine tribes, there were Ephraim, Reuben, Joseph, Dan, and Levi. So were there 14 tribes then?

It's an interesting topic, i would be interested to see what other people's opinions are on this.