I've been told by a knowledgeable person that the Autosomal DNA test decreases in value from the person taking the test backward and is of little value past five generatins whereas the YDNA test can cover a much longer period but is narrower in scope. A wikipedia article at: http://en.wikipedia.org/wiki/Genealogical_DNA_test does not appear to explain that. If in doubt check with someone with more authoritative information than I have. George