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 7th January 2018, 04:30 PM
keyhook keyhook is offline
FTDNA Customer
 
Join Date: Sep 2017
Posts: 14
Question "x-match" means that the connection is coming from your mother?

I'm a man, and I would like to understand better my "x-matches". I suppose they are coming from my mother. Or not?

Thank you a lot for helping so much in this forum!
Reply With Quote
  #2  
Old 7th January 2018, 04:50 PM
KATM KATM is offline
mtDNA: K1a3 | Y-DNA: R-L1308*
 
Join Date: Nov 2012
Location: Mid-Atlantic coast, U.S.A.
Posts: 1,078
Since you are male, yes, your X-matches will be from certain ancestors in your mother's side of your tree, but not all of her ancestors. Your father gave you your Y-chromosome, but no X-chromosome, so none of his ancestors contributed to your X.

I made a post a long time ago, with more links about the X chromosome than you could shake a stick at (well, figuratively speaking, at least). Try the two under "Learn about the X-Chromosome," and some of the charts in that post, to help you visualize the ancestors who could contribute to your X-chromosome.
Reply With Quote
  #3  
Old 7th January 2018, 04:57 PM
keyhook keyhook is offline
FTDNA Customer
 
Join Date: Sep 2017
Posts: 14
I was asking because from my father side I've got a couple of "x-matches" and it is difficult to understand why.

Thank you for your very helpful post!



Quote:
Originally Posted by KATM View Post
Since you are male, yes, your X-matches will be from certain ancestors in your mother's side of your tree, but not all of her ancestors. Your father gave you your Y-chromosome, but no X-chromosome, so none of his ancestors contributed to your X.

I made a post a long time ago, with more links about the X chromosome than you could shake a stick at (well, figuratively speaking, at least). Try the two under "Learn about the X-Chromosome," and some of the charts in that post, to help you visualize the ancestors who could contribute to your X-chromosome.
Reply With Quote
  #4  
Old 7th January 2018, 05:12 PM
prairielad prairielad is offline
FTDNA Customer
 
Join Date: Feb 2011
Location: Canada
Posts: 2,007
FTDNA will declare an X match for all segments down to 1cM/500SNP.
Majority of segments under 7cM tend to be false positive.

Are the X segments for these paternal matches under 7cM?

You can get segments sizes by viewing match in chromosome browser and clicking on View in table
Reply With Quote
  #5  
Old 28th April 2018, 01:18 PM
Susanna Susanna is offline
FTDNA Customer
 
Join Date: Jul 2017
Posts: 6
False positive for X match

Quote:
Originally Posted by prairielad View Post
FTDNA will declare an X match for all segments down to 1cM/500SNP.
Majority of segments under 7cM tend to be false positive.

Are the X segments for these paternal matches under 7cM?

You can get segments sizes by viewing match in chromosome browser and clicking on View in table
That answered my question I came here to get help with! I'm lucky that I unlocked chromosome browsing on the person whose DNA I'm researching. Should FTDNA not give a little disclaimer about this on the Family Finder - Matches page?!
Reply With Quote
  #6  
Old 28th April 2018, 03:52 PM
John McCoy John McCoy is offline
FTDNA Customer
 
Join Date: Nov 2013
Posts: 661
I agree! FTDNA and other vendors could do a much better job of putting some plain-language context around the results. A novice who is dumped into genetic genealogy will lack context, which, in this subject, is extremely important. It would help immensely if we could all go back in time and pay attention in high school or college biology during the unit on meiosis.
Reply With Quote
  #7  
Old 29th April 2018, 03:51 AM
Jomid59 Jomid59 is offline
FTDNA Customer
 
Join Date: Mar 2012
Location: Earth
Posts: 143
Does anyone know if ftdna report 48xxxy syndrome to the customer?
Reply With Quote
  #8  
Old 29th April 2018, 05:56 AM
georgian1950 georgian1950 is online now
FTDNA Customer
 
Join Date: Jun 2012
Posts: 735
Quote:
Originally Posted by prairielad View Post
FTDNA will declare an X match for all segments down to 1cM/500SNP.
Majority of segments under 7cM tend to be false positive.
This is something that everyone has wrong.

When I was weighing how low you can go on your parameters, I came up with this idea. For a given set of parameters, say x SNP's and y minimum segment size in cM's, if you can find any two kits that do not match, the chances that those parameters would cause any false positives in comparing any two kits is practically nil. Those parameters are just not spewing forth false matches stochastically.

So, why do we have all of the matching segments which defy explanation? They come from the parents sharing a common ancestor and the DNA from both comes together to reconstruct a segment of that common ancestor's DNA.

Given the nature of males not passing a X-chromosome to a son, I can find pairs of kits that do not produce any matching segments using parameters as low as 100 SNP's and 1.0 cM minimum segment.

As for showing a matching X segment believed to be on a male's father's side, it comes from the mother having a common ancestor on the father's side, possibly even being a reconstructed segment from DNA of both of her parents.

Basically X-DNA matches are not worth the time of day (even though they are not false-positive), except for cases within just the first few generations (where total amount of match may give a clue to the nature of the relationship). Spending your time on the other 22 chromosomes is a better use of time and effort.

Jack Wyatt

Last edited by georgian1950; 29th April 2018 at 06:09 AM. Reason: clarity
Reply With Quote
  #9  
Old 30th April 2018, 12:08 PM
Susanna Susanna is offline
FTDNA Customer
 
Join Date: Jul 2017
Posts: 6
Here are the details on my case re false positive for X match:

My FIL has two very good matches on each side. GEDmatch tells me that my FIL's parents were not related to each other.

His paternal side match is a half great-niece, confirmed also through family tree research, with 322 cM in common.

His maternal side match is also a half great-niece, also confirmed through family tree research, with 447 cM in common.

No problems here. But then comes a match, an unknown female person with 143 cM in common. This person shows as an X match and a "match in common" with the niece on the father's side, and I know this X match cannot be valid. So I check the chromosome browser and the X match doesn't show until I move the option down to 1 plus cM.

I was actually ok at biology and I remember meiosis. I just don't see what the utility is for making "X match" its own column on the Family Finder Matches page if it will be false a great deal of the time. Thanks!
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
Comments please, on "half" and "true" siblings clintonslayton76 Family Finder Basics 2 25th October 2016 07:06 AM
Family Finder Match Not Visible Through "Normal" Means hokiejane Family Finder Advanced Topics 3 14th March 2015 12:25 PM
Ad explanation to "My Matches" list below "Haplotree" East-Iberian Features Requests & Bug Reports Area 0 6th January 2010 11:57 PM
"DiMaggio" coming from the Albanian name "Dhima" jr76x DNA and Genealogy for Beginners 12 10th May 2008 09:27 PM


All times are GMT -5. The time now is 06:09 PM.


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.