Go Back   Family Tree DNA Forums > Universal Lineage Testing (Autosomal DNA) > Family Finder Advanced Topics

Family Finder Advanced Topics Advanced discussion about Family Tree DNA's Family Finder Product.

Thread Tools Display Modes
Old 18th July 2017, 06:05 PM
MoberlyDrake MoberlyDrake is offline
mtDNA: T2b5 | Y-DNA: J-M172
Join Date: May 2010
Posts: 1,531
Siblings - Matches In Common

My cousin has 594 matches. Of that number she shares only 134 with her full brother. Isn't that an uncommonly low ratio for shared matches between siblings? Her brother has a total of 534 matches.

The sister shares 105 matches with her aunt, and the brother shares 120.

With their uncle, the sister shares 44 matches, the brother shares 36.

With me (their double cousin), the sister shares 67 and the brother shares 95.

It just seems like the number of matches they share with each other is very low.
Reply With Quote
Old 19th July 2017, 09:37 AM
John McCoy John McCoy is offline
FTDNA Customer
Join Date: Nov 2013
Posts: 697
If the matches are weak (in the 4th cousin range, for example), your observation would be less significant than if the matches are stronger. However, the most meaningful comparison would be that of the two siblings with each other, particularly using a tool that can distinguish between full and half siblings, such as the One-to-One comparison tool on GEDmatch with the graphics option.
Reply With Quote
Old 19th July 2017, 01:04 PM
MoberlyDrake MoberlyDrake is offline
mtDNA: T2b5 | Y-DNA: J-M172
Join Date: May 2010
Posts: 1,531
Oh, they are really full siblings! The amount of DNA they share with each other (2,575 cM) and with me (their double cousin), and with my parents (the aunt and uncle in my post)proves that without the slightest doubt.

I just think it must be rather unusual for siblings to have so few matches in common. To have 120 matches in common with your aunt and only 134 in common with your sister seems a bit strange.

Last edited by MoberlyDrake; 19th July 2017 at 01:09 PM.
Reply With Quote
Old 19th July 2017, 04:17 PM
ech124 ech124 is offline
FTDNA Customer
Join Date: Jul 2011
Posts: 220
Your stats made me curious. About 5 years ago, I studied several sets of siblings and the match patterns. There was some variation of course, but very generally the pattern was that siblings would share about two thirds of their FTDNA matches and one third was unique.

I just revisited this study and found the match pattern has flipped. Those same siblings now show one third in common and two thirds are unique.

Nothing has changed about the DNA of the siblings, but the FTDNA database has obviously changed significantly. My new theory is that there have been a massive influx of transfer kits. These transfers have altered the nature of the database, because a lot of these kits have match cutoffs at about the third cousin level. Because these transfer kits are not subject to complete matching (just partial matching), you cannot make apple to apple comparisons when you generalize about overall matching numbers. It is extremely easy to fall on the wrong side of the cutoff point at a third cousin level.

I am not overly concerned with the transfers because, in my opinion, having additional partial matching is better than not having the additional kits in the database.

Last edited by ech124; 19th July 2017 at 04:19 PM. Reason: grammar
Reply With Quote
Old 20th July 2017, 01:44 PM
jimbirk jimbirk is offline
FTDNA Customer
Join Date: Apr 2017
Posts: 55
My full brother and I have both tested at FTDNA.

I have 917 matches, he has 704 matches and we share 254 matches (36%).

As for the difference in number of matches I have 3 pileup zones with over 120 matches and my brother has no pileup zones.

No other close relatives have tested.
Reply With Quote
Old 20th July 2017, 03:15 PM
MoberlyDrake MoberlyDrake is offline
mtDNA: T2b5 | Y-DNA: J-M172
Join Date: May 2010
Posts: 1,531
Pileup zones may be part of the problem. The brother has one with about 140 matches and the sister has one with about 183 matches, only in her case, it looks like a few may be matching on the chromosome she received from her Italian mother.
Reply With Quote


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
Siblings & Whole Chromosome matches Canyon Wolf Family Finder Advanced Topics 24 22nd December 2016 03:40 PM
'In Common' does not show both siblings. Juanita Family Finder Advanced Topics 2 29th July 2016 04:30 AM
X Matches for siblings hudsonh X-DNA Basics 2 24th November 2014 06:58 AM
Matches between Siblings prairielad Family Finder Advanced Topics 1 11th August 2012 04:07 PM
Is it common for siblings not to share matches? Frederator Family Finder Advanced Topics 8 9th July 2011 08:26 PM

All times are GMT -5. The time now is 12:15 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.