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.

She is one of twins, other is male, and she's definitely not a niece. An older sister will soon be doing an Ancestry test too. Wouldn't it be a surprise if I turned out to be the one with a different father as a pp had suggested!

Ancestry is accurate in my view, it correctly identified the med region my family are from, I’m British but my family are not, and it also identified many family members I know,

my mother died in very tragic circumstances, not in the uk or my families country, About 4 months after my results, it told me it had a hint about her, and it was the newspaper articles around her death, which means now I know the full detail, as I could then research further as it all gave names and places ( yes I wanted to know). I couldn’t quite beleive it.

I do agree with others, it’s not something anyone should do lightly, but make sure you’re prepared for anything like this.

its lightly you’re uncovering a family secret op, and it may not be the secret you think.

Sounds like you have different Dad's then.

You get 50 of each of your parents DNA. on average full siblings get about half the same and half different from their siblings. But you could get completely different halves, you could get the same halves. The sperm that made you, had a twin that had absolutely no shared DNA with yours. Men make trillions of sperm splitting the same 46 chromosomes, there'll be plenty with identical DNA and plenty with no shared DNA at all.

Without having your parents DNA you can't verify you're both related to both parents. But you also can't verify you're not. You just got different parts of your parents DNA. This doesn't need to change anything

My youngest sister has three regions in the very large country of my father's birth, compared to my one. Hers are neighbouring my own, and AI has said that re dna, it's possible that people have moved across regions. I do want to get to the bottom of the mystery, as while improbable, there's still a possibly slim chance that she is my full sibling.

It's now more intellectual curiosity as nothing will change our relationship and our parents have passed away.

You said your sister was a twin, would your brother be willing to take a DNA test?

I haven't mentioned my match results to the family as trying to research on my own first.

These tests are mediocre at identifying ethnicity but they are excellent at matching.
I suggest you stop thinking about ethnicity & just think about matches.
Your sister knows the situation so no shocks for you to reveal to her (phew).
On Ancestry you can find your "mutual matches", you & your sis.
It sounds very likely you have different fathers.
If you sort by closest matches on your accounts (set up 2 laptops to see the results side by side for each account)...
You'll see people not listed both places, probably.

Whether you want to find out more to figure out who was child of the man you consider your dad and who wasn't, only you can decide how much you want to know.

There is a good Radio 4 programme about these decisions and puzzles. "the Gift." They had twin women who had different dads recently. Might help you puzzle thru how you feel or want to do, to have a listen to the podcast version.

ps: there are literally experts who would work out in a few hours who had the different dad or some more info for you, not very expensive. If you don't enjoy investigating for yourself.

@lljkk can you post a link please?

My dad did that test and he found out he had another son

Mine was spot on for ethnicity, have you anything to back up they are mediocre for it?

When I did 23andMe, i understood that there is absolutely no doubt at all, and no crossover, between the percentage of DNA shared if someone is a full sibling or if someone is a half sibling. Ethnicity/origins is totally irrelevant. What’s relevant is the percentage shared with the sibling. If the site you used works the same way as 23 and me, there is no chance at all that you are full siblings.

a full sibling is 38-61% shared:
customercare.23andme.com/hc/en-us/articles/212170668-Average-Percent-DNA-Shared-Between-Relatives
Your result is firmly in the half sibling range.

I hate these sites, family are the people around you who love you and support you as you grow. I think these sites and the focus on genes just goes against all of that. Surely it would be better to just leave it and move on?

If only all our lives were like that, eh.

That is total head in the sand behavior IMO. The sites are great. They provide truth and facts.

I did my entire family on there. My mum, siblings, husband and kids. Partly because following my parents’ divorce my dad told my sister that he wasn’t her father. A big fat lie, proven to be a lie by the DNA test.

I disagree. I was adopted, not finding out about my genes is not putting my head in the sand, it's understanding the real meaning of family. Genes just aren't important in terms of who you view as family.

Once you are an adult you can choose who to surround yourself with. DNA tears aren't going to help with that.

I think adoption is a different situation - compared to ours where my father who had brought us up from birth then denied being the father of one of us as a weapon during divorce. This was cleared up quickly and accurately by dna testing.

OP - you do not have to pay someone to help you, there are volunteers who will do so for free. They are variable quality but this isnt a difficult problem (e.g where you want to find the parent of an illegitimate ancestor born in 1840) so it's very unlikely you need a professional and some are as good or better than some professionals.

I’m not sure what you’re talking about. Who is crying, and who is surrounding themselves with people they find on ancestry?

people have their own reasons, their own lives, try to respect that.

I disagree.

As I've said more than once, nothing will change our relationship. However, I would love to reconnect with family on my dad's side. Three siblings have visited close family members in their native country, and as young adults, we used to be in contact. We lost touch after they moved when the building they lived had to be demolished. It's a huge country, his native province alone has over ten million people, and none of us is a speaker of 'our' dad's native language.

The problem is compounded after one of my siblings threw away dad's original passport, after his funeral so I can't go to an embassy for help as the family name has various spellings in English. To this day she can't say why she even did that.

Back to explain to @Hiddeninthetrees that it's not about genes but about finding extended/lost family, with dna being the means to achieve that through matches.

How could a woman have no matching DNA to her children (and have them taken away) @Paytovote ?

This was answered up post by:

selffellatingouroborosofhate · 17/05/2026 19:11