X-chromosome testing

Changes Made 4 Sep 2018

Opening sentence was, "X-chromosome testing is included in 23andMe's personal genomic service and deCODE genetics' offerings." To my knowledge, deCODE, an Amgen company in Iceland, sold its DTC "deCODEme" product from 2007 to 2013, but discontinued it and stopped selling any personal DNA testing as of January 2013 (https://www.decode.com/). I modified the opening to note that X sampling occurs by default with all popular DTC autosomal tests, and removed reference to deCODE.

There seems to be a persistent misunderstanding in some quarters that X-chromosome data can be used without associated autosomal matching for genealogical MRCA identification. No doubt this is a confusion with uniparental mtDNA simply because xDNA displays a unique inheritance chain. I added one line to hopefully clarify that no testing or reporting company considers xDNA alone, without autosomal matching, to be genealogically indicative of an MRCA.

I removed reference to FTDNA as offering X-STR testing. I thought it had been discontinued, and confirmed today with Katy R., FTDNA Quality Assurance Supervisor: "We no longer offer X-STR testing and stopped offering it earlier this summer."

Removed this link from the Resources section: https://www.familytreedna.com/learn/test-types/x-chromosome-x-dna-str-testing-will-learn/ The link, following discontinuation of X-STR testing, now automatically redirects to the default FTDNA help launch page. Ed Williams (talk) 20:19, 4 September 2018 (EDT)

• Many thanks for making these changes. It is much appreciated. I've just made a few more edits to clarify matters further. I've removed the line about no company considering xDNA alone. Although xDNA does have a unique inheritance pattern, it behaves in all other ways just like the autosomes. The vast majority of our matches are on single chromosomes and a proportion of these matches will be on the X-chromosome and will therefore not be accompanied by a match on an autosome. It's just a shame that no company, apart from GEDmatch, provides a proper report for X-matching. The difficult with single segment matches is we have no easy way to determine the age of the segment. If you match on a single segment you could be 6th cousins or you could be 30th cousins.DebbieKennett (talk) 05:33, 5 September 2018 (EDT)

Thanks for cleaning up after me so quickly, Debbie.  :-) And thank you for reminding me that the X-chromosome's hemizygosity in males equates to it being "naturally phased." That's a perfect way to describe it, and conveys that a male-to-male distant cousin X-match comes with no other special super powers granting it immunity from triangulation or deeper investigation of the evidence. Ed Williams (talk) 10:25, 5 September 2018 (EDT)

• I didn't come up with the term naturally phased. I've seen it crop up elsewhere but it's a good way of describing the process.DebbieKennett (talk) 13:10, 5 September 2018 (EDT)

Dead link

Could not find any replacement URL for this, so deleted it.