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

X-DNA Advanced Advanced topics about X-Chromosome matching and anthropologic blocks based on SNPs and/or STRs.

Reply
 
Thread Tools Display Modes
  #1  
Old 26th June 2015, 03:21 PM
alice alice is offline
FTDNA Customer
 
Join Date: Jun 2015
Posts: 7
Confusing x-matches

The attached table summarizes a group of matches with Person H, who is a female and recent autosomal match with persons A-G. I am looking for help in this forum in understanding two issues:

1. How is it possible for two children to have larger matches with person H than their fathers have?

2. How is it possible for two daughters of person A to have x-matches with person H when their father does not have an x-match with H and all the autosomal matches in the table point to A's father's father's side, not his father's mother's side? In other words, the x-matches and the autosomal matches seem to point to different sides of the family in looking for the MRCA.

In addition to the matches shown in the table, there is a further group of three people who match persons A-H Family Finder. All three of these people are also on A's father's father's side.
Attached Files
File Type: doc Anderson Matches_.doc (30.0 KB, 18 views)
Reply With Quote
  #2  
Old 26th June 2015, 04:08 PM
KATM KATM is online now
mtDNA: K1a3 | Y-DNA: R-L1308*
 
Join Date: Nov 2012
Location: Mid-Atlantic coast, U.S.A.
Posts: 1,081
Just to make sure: are these all longest segments shared, not total cM combined sharing?

Are all the children of A in this chart from the same mother? If so, are both parents possibly from the same ancestral group (endogomous)?

It's possible that H is related in some way to both the father A, and the children's mother. The gap in cM between A and daughter C (almost 10 cM) certainly seems to me to be too much to blame on "fuzziness" in results, or rounding; I'm not sure if G's larger share (about 4 cM) to H than F's could be explained by rounding/fuzziness or not.

Have any of these matches uploaded to Gedmatch.com? You could check the "Are your parents related?" tool there, if the children's mother has also been tested. But I suppose you would have shown results for the mother if she'd been tested, too.

I hope the experts will chime in on this one.

Last edited by KATM; 26th June 2015 at 04:13 PM. Reason: added wording for clarity
Reply With Quote
  #3  
Old 26th June 2015, 06:14 PM
prairielad prairielad is offline
FTDNA Customer
 
Join Date: Feb 2011
Location: Canada
Posts: 2,007
What is the X amount shared between each daughter and match?

X match may be IBS (Identical by State/false). Each daughter has two X's, if these are small segments, algorithm may be picking values from both their X's and creating a false segment. If match is also female, there is a greater chance that these small segments will be IBS as algorithm will be choosing from female matches 2 X's value and daughters 2 X's values.

What is the chromosome and segment start/stop points of persons F and G to this match?

Each chromosomes comes in pairs, algorithm does not know what value goes to which single chromosome of the pair, it just looks for a string of single continuous values in a consecutive run of SNP which have 2 values each (maternal and paternal chromosome)
Again the son (G) may have a bunch of IBS segments giving him the appearance of sharing more DNA with match.

What is the longest segment start/stop points for this match with Father (F) and Son (G)?

If sons longest segment matches with match where his father matches, but is longer, then the beginning or end will most likely be IBS. Fathers segment will be the truer shared longest segment with this match.

If you use GEdmatch (as well as this match), phase father and son (F and G) and compare sons phased file with this match and you will probably see less DNA shared, and probably no DNA share with his maternal file.

Last edited by prairielad; 26th June 2015 at 06:27 PM.
Reply With Quote
  #4  
Old 26th June 2015, 07:00 PM
prairielad prairielad is offline
FTDNA Customer
 
Join Date: Feb 2011
Location: Canada
Posts: 2,007
Quote:
Originally Posted by prairielad View Post

.....

What is the chromosome and segment start/stop points of persons F and G to this match?

Each chromosomes comes in pairs, algorithm does not know what value goes to which single chromosome of the pair, it just looks for a string of single continuous values in a consecutive run of SNP which have 2 values each (maternal and paternal chromosome)
Again the son (G) may have a bunch of IBS segments giving him the appearance of sharing more DNA with match.

What is the longest segment start/stop points for this match with Father (F) and Son (G)?

If sons longest segment matches with match where his father matches, but is longer, then the beginning or end will most likely be IBS. Fathers segment will be the truer shared longest segment with this match.

If you use GEdmatch (as well as this match), phase father and son (F and G) and compare sons phased file with this match and you will probably see less DNA shared, and probably no DNA share with his maternal file.
Same would apply for Daughter C and Father A
Reply With Quote
  #5  
Old 26th June 2015, 07:29 PM
prairielad prairielad is offline
FTDNA Customer
 
Join Date: Feb 2011
Location: Canada
Posts: 2,007
If all files are on Gedmatch...

you can even lower the threshold matching in Gedmatch's one to one when comparing these phased files with match to match the cM and SNP sizes that show for these small segments in FTDNA's data.
If it does not find them at Gedmatch in these phased files (maternal file and paternal file) you will know that it was combining values from both to create a false segment.
Reply With Quote
  #6  
Old 28th June 2015, 08:14 AM
alice alice is offline
FTDNA Customer
 
Join Date: Jun 2015
Posts: 7
Further to "confusing x-matches"

Thanks to those who replied.

To clarify, the cM numbers given were totals, not longest segment. All matches in this case share a continuous segment on chr. 15 ranging in size from 7.73 cM to 30 cM, in addition to smaller matches.

The children of A all have the same mother. A and his wife are both on GEDmatch, and the parents are shown as not related to one another.

Father F and son G share an identical segment of 13.01 cM with H on chr. 15 (position 30195523 to 40121632). I assume the somewhat larger match of son G with H is just random IBS?

The x-matches of B and C with H are 5.42 and 3.16 cM respectively, with the 3.16 falling inside the 5.2 segment. I followed the suggestion to generate phased files. These show no match between H and the maternal side of B. They show an estimated 4.8 generations between B and H.

Am I correct in believing this confirms that the x-match is random / IBS and results from the test not differentiating between the two x-chromosomes of a female? If so, this leads to a further question: is it not possible for FTDNA to show two separate analyses of a female's two copies of the x-chromosome?

Regarding the larger match between C and H than between C's father, A, and H: the matching largest segment on chr. 15 is identical for A and C: 11.95cM. Daughter C has a couple of additional small segments matching H that her father does not have. Should I take these to be IBS?

What I am concluding from all this so far is that the x-match turns out not to be real, and that I am confirmed in continuing to seek the MRCA between H and the others on the line originally suspected: C's father's father's line.
If anyone sees an error in this reasoning, please advise.

Thanks again to all.
Reply With Quote
  #7  
Old 28th June 2015, 08:48 AM
dna dna is offline
FTDNA Customer
 
Join Date: Aug 2014
Posts: 2,963
Quote:
Originally Posted by alice View Post
[----] is it not possible for FTDNA to show two separate analyses of a female's two copies of the x-chromosome? [----]
It is not possible to do that for the autosomal DNA and the female X chromosome.

W. (Mr.)
Reply With Quote
  #8  
Old 28th June 2015, 09:04 AM
prairielad prairielad is offline
FTDNA Customer
 
Join Date: Feb 2011
Location: Canada
Posts: 2,007
Quote:
Originally Posted by alice View Post

......

Am I correct in believing this confirms that the x-match is random / IBS and results from the test not differentiating between the two x-chromosomes of a female? If so, this leads to a further question: is it not possible for FTDNA to show two separate analyses of a female's two copies of the x-chromosome?

.......
Gedmatch has the X one to one also, If you are able to create phased files for the daughters, you should be able to verify.(would need to lower gedmatch's default thresholds to match FTDNA SNP and cM size of these X segments)

As for FTDNA to show separate analyses of females two copies of X (or anyone's two copies of chromosomes 1 thru 22), they could, to a degree, if they allowed phasing between parent/child relationships.
Reply With Quote
  #9  
Old 28th June 2015, 09:37 AM
dna dna is offline
FTDNA Customer
 
Join Date: Aug 2014
Posts: 2,963
Quote:
Originally Posted by prairielad View Post
[----] As for FTDNA to show separate analyses of females two copies of X (or anyone's two copies of chromosomes 1 thru 22), they could, to a degree, if they allowed phasing between parent/child relationships.
Alice, that is correct, but FTDNA cannot do that as a result of a DNA test...

Mr. W.
Reply With Quote
  #10  
Old 28th June 2015, 10:24 AM
prairielad prairielad is offline
FTDNA Customer
 
Join Date: Feb 2011
Location: Canada
Posts: 2,007
I was just on Gedmatch because I was curious if the phasing utility phases the X chromosome.

By the looks of it for males it does it incorrectly for FTDNA's X raw data, as it is given as double values (ie AA when it is only A, males only have 1 X)

My phased paternal file shows a full X share with my father, as well as a full X match between my maternal and paternal phased files. I (male) only have 1 X from my mother.

So depending on sex of phased files using, keep that in mind that you may be unable to determine when comparing X data with phased files (males phased data)

It does show the correct amounts when I compare my sisters phased files against each other in X one to one. Full share on paternal files, partial share on maternal files
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
confusing matches ldp40 Family Finder Basics 1 3rd December 2014 07:24 PM
percentages in Y-DNA TiP Report confusing to me LauraLou DNA and Genealogy for Beginners 1 2nd December 2014 07:52 PM
Confusing Results Paul Burns The Genographic Project 1 10th March 2014 10:21 AM
Very Confusing Chromosome Browser results mikelandwehr Family Finder Advanced Topics 0 9th September 2013 03:38 PM
confusing results and infidelity.... dnaval DNA and Genealogy for Beginners 9 14th August 2007 10:35 AM


All times are GMT -5. The time now is 09:42 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.