A friend of mine recently emailed enthusiastically saying new AncestryDNA test results showed a match with a 5th to 8th cousin with a fairly rare surname. It could be a real connection, and one hates to stifle enthusiasm, but that's so distant possible relationship it's only a faint hope.
Today along came a link to a PowerPoint presentation by Tim Janzen where he lists some misconceptions of chromosome mapping, the first relevant to this situation being:
Just be cause you find a surname in common (or even a shared ancestor) with one of your matches doesn’t necessarily mean that the DNA segment you share in common was passed down from an ancestor with that surname or the shared ancestor.AncestryDNA doesn't provide a facility for chromosome mapping. unless you transfer the raw data to FTDNA or a utility like GEDmatch, and can persuade your match to do the same, so AncestryDNA just leaves you with the, likely, false hope.
Chromosome mapping helps you sort these issues out quickly and efficiently. It prevents a lot of “wild goose chases”!
You may be interested in reviewing all Tim's most recent presentation PowerPoints from the recent Southern California Genealogical Society's Jamboree. They may be downloaded from
http://tinyurl.com/pedxr4b (Examples of How Autosomal DNA Testing Solved Genealogical Questions),
http://tinyurl.com/pjg4akw (Autosomal DNA Chromosome Mapping Workshop),
http://tinyurl.com/nzkhhvw (Programs to Help You Analyze Your Autosomal DNA Data),
http://tinyurl.com/ntbe3zs (Using Autosomal DNA Testing as a Means to Trace Your Family Tree).