Confirming possible half sibling from AncestryDNA?

Question

It took a few months to process this shocking news from my dna results from ancestry. I am a new at this & did the test with my daughter for fun.

Imagine my surprise when someone contacted me saying we are very closely matched & she was perplexed at my #'s. She is experienced searching her family tree with 2000+ people. We share 1499 cm across 47 segments. I also share 758 cm with her son. My daughter also matched with her family. The match is an only child.

I saw no dna matches on my father's side.

About a dozen I recognized from my mother's side.

We texted back & forth & saw that our families lived in the same town where I was born. I have other siblings, I am in the middle . One sister is being tested. The match is an only child.

My research suggests she is my half sibling with her father being my biological father. She is now implying its her father's brother. He doesn't have children. All parents are deceased and both of us are over 60 wirh 10 yrs between us.

The fathers sister has children & one of his kids matches me as a 2nd cousin @ 243cms.. my ?..if it was the father's brother wouldnt she came up as a 1st cousin.. my dad will always be my dad but I'm not going to keep it a secret from my children for long..

I personally grew up around my fathers family which according to DNA I'm now not related to any of them at all..

I will know more when my sister gets her results back in a few weeks & I will download to Gedmatch. I should also mention that I have a twin brother that I was hoping to have his support to deal with this but only 2 sisters know and say I can't tell him b/c he'll be crushed as he carries my dads name & has 2 sons .. its been suggested I don't tell the other 3 sibs either ..Do most people in this situation keep it to themselves.?

Answer 1

That's a lot to deal with.

Hold off on the announcements for now. It's very VERY rare, but sometimes a company makes a mistake. It's also possible you might be right about the NPE (non-parental event aka not parent expected) but wrong about the details.

You need more people to test. Has anyone, second cousin or closer, from your dad's family tested? With any testing service. Get your raw data on Gedmatch and look around. If someone has tested with a place besides where you tested, you can compare DNA on Gedmatch. It's free.

It looks really likely that your conclusion (that your dad is not your bio-dad but your mom is your bio-mom) is correct. But take that last step to be sure. If you do not have any segments in common with someone who is a second cousin or closer, then there is a NPE involved. Most but not all 3rd cousins will show a match.

If this woman is your half sister, the cM range will be 1317-2312. If it's her uncle who is your birth dad, then she and you are first cousins and the cM range will be 553-1225. Your actual match is 1499 cM. You are NOT first cousins.

Do not go by AncestryDNA's relationship predictions. Remember, there are multiple possible relationships for every given cM match. Figure out which ones are possible then work with the paper trail/reality to eliminate some of them.

Use this site: http://thegeneticgenealogist.com/wp-content/uploads/2017/08/Relationship_Chart_FINAL_August_2017.jpg

For 1499 cM, your only choices are: grandparent (great grandparent is just outside the range), great aunt/uncle, aunt/uncle (half aunt/uncle is just outside the range), and half sibling. Things that are just outside the range are possible because the ranges were determined by a very large survey of known relationships. There can be outliers not accounted for. But it's unlikely.

Obviously, you can rule out grandparent (and great grandparent). But half sibling is not the only choice left. Maybe your bio-father is this woman's brother (it could possibly be her half brother).

Do keep in mind that not all NPE's are something bad. Our minds may immediately go to cheating but there are other possibilities. Sperm donation has been a thing for a very long time. Some martial relationships have "arrangements" and such that maybe you don't want to hear about but aren't infidelity. And, the worst case, not all encounters are consensual. You don't know why this happened and I urge you to consider you may never know and to be gentle with your memories of your mom.

Good luck and, if you feel comfortable doing so, please post the outcome (or other questions) here. I'd like to hear how this turns out. Good luck.

Answer 2

Do you tell your other siblings that only you & a twin brother are not their dads biological child but are now a half sibling & would it cause more problems.?