Ancestry DNA says my youngest sister may be a half sibling

[ancestrydnashock]

I got my updated Ancestry DNA results and only have 26% dna in common with my youngest sister. We are of multiple ethnicities; my dad is 100% X while my mum is multi ethnic. Mum passed away two years ago and dad died decades ago. I look like my father, while she takes after our mum, so no cause to think anything odd.

I'm didn't think much about the results at first, but then did a google search which said, while very unusual, it was possible for a full sibling to show up as a half sibling. I then asked AI and input more info, including the name of the test, then got the answer that the shared cM amount, indicated a half sibling or niece.

The only thing I had found mildly questionable before, was that my sister had 40% and not 50% X dna in her test results and that her dna was from a different part of the country, (think east, not south like mine).

To say I'm shocked is putting it mildly and I have to think about what, if anything, I do next.

Wait for the shock to wear off a bit. You don't actually have to 'do' anything, at least not for now.

I think there is a genealogy section here, and there definitely is on Reddit. You will probably get more knowledgeable answers there. Do you have any other relatives eg cousins? And like pp said, you don’t need to rush anything. But I’d be careful of taking too much attention of what chat gpt says about this. Use it as pointers for where you can get more information, or what questions to ask people rather than just believing it.

26% is half sibling
I can confirm this from experience

I have found mine that I was looking for for a while after finding out my mum was in one of those awful Magdalene laundries. The 26% on Ancestry confirmed it

Look on the bright side OP
you have grown up with them and have a relationship as sisters
No one can take that magic away from you both

Moving on
Ancestry will link up with others who have logged their dna. You may both find out more in terms of parents etc with that.

I’d be wary of jumping to conclusions because of what an AI says. She’s not necessarily a half sister rather than a full sister just because she shares only 26% DNA with you.

As pp suggested, I've had a look at relevant subs on Reddit and apparently Ancestry is the 'gold standard' in dna testing.

My dad was my mother's second husband and I actually have a known half sister whose dd is also on Ancestry. She has matched as a half niece with 11% commonality. My youngest sister's dd is showing a similar matched commonality at 12%.

I'm a sceptical person generally and want to investigate further. Nothing has changed in how I feel about any of my siblings.

I'm not sure I trust these ancestry tests. I took one with My Heritage and it went from telling me I was half Swedish to 0% and part Iranian to 0%. How does that happen?

If you think your dad might not be your youngest sister’s dad, do you have any relatives on your dad’s side already on Ancestry? If she is only a half sister to you then she won’t have any genetic link to them.

I would tread carefully. You say you are shocked but it is your sister who could be about to find out the man she thought of as her dad isn’t her biological dad. And your mum isn’t around to get the story from. Imagine how she is going to feel. Does she have access to your results? Do you discuss them so she might ask you what it means? Or is doing nothing for now at least an option?

Reddit doesn't have much good to say about My Heritage, unfortunately. I think all the kits however, have a disclaimer about using the results.

My dad was from a country that most likely doesn't use dna testing kits, as no matches came from that country.

My youngest sister and I did the tests together and have shared and discussed differences in our results and how complex genetics/gene dispersal are. We had dismissed appearance/gene differences in this way, but with the same dad, we should have both had father's dna linked to the same region of his vast birth country.

My 11% and 12% connections on ancestry are all first cousins
( they could also be half aunts/uncles)

on the basis that I know many of these first cousins I know
the 11/12 % is accurate as a first cousin

It can’t be a half or full sibling at 11%. The dna connection simply isn’t high enough.

Here are some of my dna % links.

I know who they all are so can confirm the dna connection as accurate

( tap image to see in full )

hope this helps

Ps. It makes sence that your youngest sisters dd would have an 11% connection to you

A Half sibling is around 26% dna with you
their child approx half that again at 11/13%

I think we should all have counselling before doing these tests….

Is there a possibility that it is your dad who is not who you thought? Ignore the fact you look like him, we see what we want to see. Is the known half sibling you mentioned on your mother or your father’s side?

Estimates of ethnic heritage are quite different to the accuracy of close family shared DNA.

There are various Facebook pages that could help you work out which of you has the not expected parent. Dont go on looks. It is very likely that you are half sisters but possible you could identify the missing parent, or at least the grandparents. What is possible depends on how many DNA matches you each have, how close the nearest matches are, whether they have trees.

Take time to get over the shock but screenshot the trees of any close matches immediately, they could disappear.

Radio 4 did an excellent investigation into those DNA testing kits on an episode of "Sliced Bread"...experts explain where the percentage figures come from and all is not as it seems! Worth a listen.
BBC Sounds, Sliced Bread, DNA testing kits.

The kits aren’t reliable from the pov of saying what country/ethnicity someone may be but the dna doesn’t lie when it comes to dna matches. I’m on a very good fb group. DNA detectives uk. Ask on there and tell them number of cm. I know a friend has a half sister and they share 32% of dna.
But centrimorgans is more accurate boundaries I think so that’s the number to focus on.

It would be super unlikely but it’s not impossible that something strange can occur.

I remember a woman who didn’t have any matching dna to her children and had them taken away. She actually had to live birth another and test in hospital to get them back!

But this is very rare. But if the defo half sister is also coming up low then maybe that makes sense?

It could be the OP’s sister who has a different dad. Not the OP. But yes ultimately it would be hard to know as both parents are no longer here.

OP do either of you have relatives in your matches you don’t recognise? I had half cousins on my matches and knew immediately something was up. Turns out my grandad wasn’t my grandad.

Yes, not an expert in genetics at all, it is very rare but have read it is possible for some brothers and sisters to inherit genes which mean they can seem barely related.

@ancestrydnashock Hi OP, I hope you don't mind but I've asked MNHQ to move your thread to the Genealogy topic as there will be more people with experience about dna results who can advise. 🙂

Also are your dna matches in common only on one side of your family?

It may be inaccurate.
Mine had my daughter sharing only 48% DNA with me (??)
It also told me I was 78% Scottish… I have a foreign grandparent who definitely isn’t 3% Scottish!

There is an easy way to confirm this.

It will be to do with your other matches.

You need to work out which parent is your maternal and paternal (parent 1 or parent 2), then look at your shared matches particularly the closest ones.

If you are half siblings the matches for one parent will be completely different. If they are a half siblings you will get at least some common matches.

It will be fairly easy to determine whether they are a half sibling or not.

The 48% is within normal limits for a parent/child relationship. Theoretically a child inherits 50% from each parent but dna tests don’t count very common dna segments so will potentially drop a couple of percentage.

Ancestry will calculate relationships on probability. A large age gap can confuse matters about niece v half sibling for example.

On the whole though it's not wrong - it's just the interpretation it provides - the cM value still tells the story.