In a message dated 1/31/2001 7:45:03 AM Eastern Standard Time, [email protected] writes: > Sir- > > My family is participating in the Y-Line testing coordinated by George W. > Page. I have some questions that maybe you could answer for me in laymens > terms: > > 1. If two men of the same surname have identical Y-chromosome genetic data, > it means they have a common paternal ancestor, right? But how recently? A > common ancestor within the last 500 years? 1000 years? 10,000 Years? How > far back do you have to go for the Y-chromosome genetic data of two men with > a common paternal ancestor to be different. Will the Y-chromosome genetic > data for two men with a common paternal ancestor 10,000 years ago look the > same as if they were first cousins? If so, what good is y-line testing > except to identify lines broken by adoptions? The Y-chromosome genetic content changes slightly over time. I think that out of several dozen matching Jefferson descendants in the Thomas Jefferson - Sally Hemmings study they found one male descendant who had a change by a count of one in a single marker in about 200 years. We won't know how well the Y-line testing distinguishes various Page lines until we see the results of this pilot study, but I expect that 1) There will probably be several totally unrelated Page families (after all, "Page" is a generic name, like "Smith.") 2) There will probably be several clusters of Page descendants not known to be related who in fact had a common ancestor back in the old country. If this common ancestor was far enough back, we may see slight changes in the DNA markers that will help sort out the descendants of different Page progenitors in the New World (that is, if we're really lucky). The worst-case scenario would be that every Page in the study has exactly the same DNA markers. But even that would be interesting to know... 8-) > 2. If the genetic data changes a known amount for every so many generations, > then you could tell roughly how closely two people were related. For Y-line > testing, what is this accuracy? Plus or minus how many generations? Lots of generations, I'm afraid. > Thanks very much for your help. > > Dick Hamly You have some very good questions here. Whatever we find out, this DNA study will be quite an adventure, and maybe some of your questions will be answered by the results we get. --Patricia Page Wilcox