Moderator Control Panel ]

DNA and Full Siblings

A problem shared is a problem halved. Post your brick walls here and see whether you can offer advice to others

DNA and Full Siblings

Postby eurogordi » Thu Jul 26, 2018 3:03 pm

I've just been persuaded to take a DNA test, but not being at all scientific I'm still slightly cynical about the process (although a close friend has recently taken a DNA test with excellent results).

I am one of six siblings and so, presumably, if each one of us had our DNA tested for ancestral purposes it should provide identical results... and then I read elsewhere that everyone's DNA is unique to that individual!

Would anyone like to make any comments?
Posts: 203
Joined: Thu Jan 01, 1970 12:00 am

Re: DNA and Full Siblings

Postby AdrianB38 » Thu Jul 26, 2018 4:04 pm

eurogordi wrote:... presumably, if each one of us had our DNA tested for ancestral purposes it should provide identical results...

I'm not very up on DNA, but my understanding is that the DNA of siblings is not the same. Or if it is, then you're actually identical sextuplets...

You won't even necessarily get the same ethnicity estimates - see I think each child inherits 50% of their DNA from each parent - but it's not the same 50%
Posts: 2783
Joined: Tue Jul 27, 2010 4:07 pm

Re: DNA and Full Siblings

Postby Mick Loney » Thu Jul 26, 2018 5:04 pm

Put very simply, each person gets their DNA from both their father and mother, but not exactly the same amount from each, and is rather random. You may get only 30% from your father, and 70% from your mother (i.e. favouring your mother) whereas a sibling may get their proportions the other way round.
So if you compare your DNA with your siblings, these differing proportions will show as differences between each of your DNA’s.
So yes you should see a strong match, as you both inherited your DNA from the same parents, but it won’t be the same.
Going back a generation, you may get some DNA from your paternal grandfather, whereas one of your brothers did not get any!
Mick Loney
Posts: 747
Joined: Fri Feb 18, 2011 11:39 am

Re: DNA and Full Siblings

Postby DianaCanada » Thu Jul 26, 2018 5:53 pm

My brother and I share 2563 CentiMorgans across 61 DNA segments. Falls well within the predicted range for siblings. We both tested through Ancestry. My daughter shows the typical range for parent/child as well.
Strangely, though my brother has about 50% more matches within the range to 6th cousins than I do, so glad I had his done too. The relatives I match more with are just not showing up!
Also I have 5% British, he has none. My daughter has close to none too and ALL of our ancestry goes back many generations in England though she has more Scots and Ulster Scots on her father's side. I don't find the ethnic part of their test terribly reliable. It said roughly 50% of my ancestors are from northern England (true) but then I am hardly British at all? I undestand why this is so, just wish the company would clarify it better.
Posts: 307
Joined: Fri Jun 23, 2017 11:37 am

Re: DNA and Full Siblings

Postby JaneyH » Thu Jul 26, 2018 7:13 pm

I thoroughly recommend buying / borrowing a copy of Blaine Bettinger’s book: ... ref=plSrch It’s a great beginners guide and having read and reread it I’m now beginning to understand DNA research a bit better. You’ll also find some really good blog articles on Donna Rutherford’s website:

Sent from my iPhone using WDYTYA Forum
User avatar
Posts: 609
Joined: Mon Dec 02, 2013 5:35 pm

Re: DNA and Full Siblings

Postby Mick Loney » Thu Jul 26, 2018 9:41 pm

Agree about the book, a good read and a good beginner’s introduction to using DNA for genealogy :D
Mick Loney
Posts: 747
Joined: Fri Feb 18, 2011 11:39 am

Re: DNA and Full Siblings

Postby HardWork » Fri Jul 27, 2018 5:32 pm

Who has persuaded you and what are they hoping to find out? There is more than one type of test. If you are trying to find your male line ancestry you'd be better off taking a Y DNA test in all probability than an autosomal test, but you would need to be male as only they carry Y DNA. Autosomal is more suited to finding cousin relationships and can help determine mutual direct ancestry via that. However, arguably, autosomal is less useful to anyone who has already built a family tree back about 6 generations on all lines (except maybe to prove it) as the aDNA gets diluted on with each passing generation, on average. The ethnicity element of aDNA is on the verge of faux science for most people of Western European ancestry as the terms used are vague or use descriptions that reflect modern nations rather than ancient origins. With so much movement between European peoples it is rarely possible to determine which wave one's ancestors link back to.
Having said all that, taking a test is useful because DNA outcomes work by comparison, so the more people that test, the greater chance of finding matches.
Posts: 39
Joined: Mon Feb 12, 2018 10:49 am

Re: DNA and Full Siblings

Postby ksouthall » Fri Jul 27, 2018 8:35 pm

My mum's two sisters have both taken Ancestry DNA tests. There results were as follows:

Aunt A - Ethnicity Regions: Scandinavia, Europe West, Ireland/Scotland/Wales, Iberian Peninsula
Trace Regions: Europe South, Great Britain, Finland/Northwest Russia, Middle East

Aunt B - Ethnicity Regions: Scandinavia, Great Britain, Europe West, Iberian Peninsula, Ireland/Scotland/Wales
Trace Regions: Europe East, Europe South, Caucasus

My DNA result was as follows:

Scandinavia 39%
Iberian Peninsula 13%
Europe West 5%
Ireland/Scotland/Wales 4%
Europe South 2%
Caucasus 1%
Finland/Northwest Russia <1%
Asia South <1%

However, this has been updated and I am now showing as 100% England and Wales, more specifically Southern England and Northern England & the Midlands.

My son's ethnicity has also been updated:

England and Wales - 97% (Increased by 48%)
Ireland and Scotland - 3% (Decreased by 15%)

It seems that we are no longer Vikings! I'm assuming my aunts' ethnicity has also been updated.

Anyway, one interesting thing to come out of the DNA testing is that it appears my mum and Aunt B are identical twins rather than fraternal twins, as the relationship is shown as Possible range: Parent, Child - immediate family member. Confidence: Extremely High. Relationship: M.G. is your Mother

By contrast, the relationship to Aunt B is as follows: Predicted relationship: Close Family. Possible range: Close family - 1st cousins. Confidence: Extremely High.
Posts: 1945
Joined: Tue Sep 23, 2008 7:26 pm
Location: Sussex

Return to General research queries

Who is online

Users browsing this forum: No registered users and 14 guests