Go Back   Family Tree DNA Forums > The X-Chromosome > X-DNA Basics

X-DNA Basics This forum is for newbie topics about the X-Chromosome. All may view this forum, but you must register and sign in to post.

Reply
 
Thread Tools Display Modes
  #1  
Old 24th February 2018, 10:58 AM
Werinkme Werinkme is offline
FTDNA Customer
 
Join Date: Feb 2018
Posts: 2
Dna match is a X-match in the list but not in Chromosome browser?

Hello, can anybody help me with this? I have several X-matches in my list of dna matches, who don't show up as X-match when I compare them in the chromosome browser (on the ""X"" there is no color that belongs to that person).
Does anybody know how I should interpret this? Is it a real X-match or not? Thanks, Liesbeth
Reply With Quote
  #2  
Old 24th February 2018, 01:05 PM
KATM KATM is offline
mtDNA: K1a3 | Y-DNA: R-L1308*
 
Join Date: Nov 2012
Location: Mid-Atlantic coast, U.S.A.
Posts: 1,102
The X segments for these matches of yours are probably too small to be "real"; in other words, they are not IBD (Inherited by Descent).

You may be viewing the match in the Chromosome Browser using the default setting of 5 cM. You can change that setting (a drop menu above the selected names of the matches you are comparing) to show a smaller cM comparison (1+ or 3+ cM). The matching X segment should show at 1+ cM setting.

Although FTDNA marks matches as being an "X-match," almost always it is too small in size to be inherited. The current advice is that an X segment probably needs to be at least 15 cM, if not 20 cM, to really indicate a connection; in other words, matching X segments need to be about two times the size that a similar autosomal segment would be (7 to 10 cM minimum), to be worth investigating.

Last edited by KATM; 24th February 2018 at 05:25 PM. Reason: changed "usual" to "current" in second sentence of last paragraph
Reply With Quote
  #3  
Old 24th February 2018, 02:27 PM
John McCoy John McCoy is offline
FTDNA Customer
 
Join Date: Nov 2013
Posts: 694
Also, I think X matches should be disregarded if they are not also an autosomal match. Even if you somehow managed to get the same piece of an X chromosome as someone else who is not also an autosomal match, you would have no way to work out where that X came from.
Reply With Quote
  #4  
Old 26th February 2018, 01:06 AM
Werinkme Werinkme is offline
FTDNA Customer
 
Join Date: Feb 2018
Posts: 2
Thank you both KATM and John McCoy for your answers. Yes I tried with other default setting (>1CM) and indeed they do appear now. Good to know that these small X-matches are probably not real and not very useful.
Reply With Quote
  #5  
Old 26th March 2018, 05:42 PM
MoberlyDrake MoberlyDrake is offline
mtDNA: T2b5 | Y-DNA: J-M172
 
Join Date: May 2010
Posts: 1,531
I really don't think FTDNA should label matches as X-matches unless they share a segment at least 15 cM long. It only confuses people who are new to DNA testing.
Reply With Quote
  #6  
Old 12th April 2018, 07:58 PM
mabrams mabrams is offline
FTDNA Customer
 
Join Date: Mar 2006
Posts: 194
I agree with Moberly Drake that X matches should not be shown unless 15 cM. I might be slightly more tolerant. 9 or even 7. But all those 1 to 4 cM X matches are just wrong to show.

I have 44 X matches. Only 3 are above 7 cM. One is my mother, so really 2. And just two more greater than 5 cM. Its a waste of a column. I realize women get a lot more X matches but not sure how many of them are above 7 or 15 etc.

For some reason, I do have more X matches at 23andMe and also GedMatch. I guess because they are not tied to an autosomal match. Some of them are quite decent. Many over 20, even 30 cM.

I would get rid of the X column entirely. Or post the actual cM instead of a super generic 'X-Match'. That would be useful And it would be nice to sort the column by size of cM, which does not seem to be the case to me.

Actually, I think a Tab, like for the Paternal and Maternal would be nice. (And Tabs for Y and mtDNA??)

Last edited by mabrams; 12th April 2018 at 08:09 PM.
Reply With Quote
  #7  
Old 13th April 2018, 05:06 PM
John McCoy John McCoy is offline
FTDNA Customer
 
Join Date: Nov 2013
Posts: 694
My take on the situation is that X matches are virtually useless unless there is also a very strong autosomal match. Let's suppose that you have a 30 cM X match and NO autosomal match. How do you proceed? Since the relationship must be at least on the order of 3rd cousins or even more remote, due to the absence of autosomal matching segments, the X match could come from almost any ancestor, except for those that can be ruled out based on your gender and the way the X chromosome is inherited. But there are still too many possibilities, unless you have other information. You will be no further ahead than if you had no X match at all.

Also, the mention of GEDmatch rings a bell. The number of X matches that females will find on the One-to-Many report in GEDmatch is grossly inflated. Most of them, sometimes around 90 percent, will not be scored as matches with the X One-to-One comparison tool. I'm not sure what the One-to-Many matching algorithm is doing, but it is definitely not working well for females on the X chromosome! Beware!
Reply With Quote
Reply

Bookmarks


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Fam Finder match list vs. ydna match list (no common names) TomHerman Family Finder Basics 16 25th August 2015 05:46 PM
Got an email from a match but they aren't in my match list! Carla Features Requests & Bug Reports Area 6 3rd May 2015 07:51 AM
Chromosome Browser - one match contained in another manoss Family Finder Advanced Topics 2 18th October 2012 12:58 PM
31cM - Not In Finder Match Match List shandy4473 Family Finder Advanced Topics 3 3rd May 2012 11:13 PM
Match In Child List But Not In Either Parent List!!!!! shandy4473 Family Finder Advanced Topics 35 3rd January 2012 03:53 PM


All times are GMT -5. The time now is 11:35 AM.


Family Tree DNA - World Headquarters

1445 North Loop West, Suite 820
Houston, Texas 77008, USA

Phone: (713) 868-1438 | Fax: (832) 201-7147
Copyright 2001-2010 Genealogy by Genetics, Ltd.
Powered by vBulletin® Version 3.8.4
Copyright ©2000 - 2018, Jelsoft Enterprises Ltd.