This is from The Clan Donald heritage site - If you are fortunate enough to have family tradition that tells you with which branch your ancestors associated, you may choose to wear that tartan. It is not necessary that you trace your genealogy directly back to a Clan Donald branch chief to justify wearing the branch tartan (if you can do that you could be in line to be chief). There were considerable movements and marriages that weren't confined to Clan Donald branches or lands. It was a strong Celtic traditional value to seek a bride outside the immediate clan which not only prevented consanguinity (inbreeding problems experienced by feudal nobility, such as hemophilia), but strengthened the clan by expanding it's influence. This Celtic trait of your ancestors may make the decision of which MacDonald tartan to claim as your own more complicated and explain why the common Scottish answer to the question, "Which tartan should I wear?" is "Which one do you like?"

http://www.clandonald-heritage.com/i...d=38&Itemid=57

I shall do more research on this and will post again soon.