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I was given an AncestryDNA test as a Christmas gift and I took the test. I was matched with several people that I didn’t know but I assumed they were people on my dad’s side who I knew absolutely nothing about. Not even his name.

After doing some research into the matches, I got info from one of my cousin matches about some other family members and reached out someone I thought I was related to. I asked him to do an AncestryDNA test and he did. His results showed that we are close family. We have 1845cM I believe he is my half brother.

We both share a match with someone else but our cM numbers are totally different. Mine Is 949 cM with this woman and his read 1449cM with her. I know for certain that he is her half uncle because her dad is his brother. What’s throwing me off is the fact that, if he is my half brother, then that would make me her half aunt.

He shared cM with him it making me believe that he’s not my Half brother. I’m really trying to figure this all out but I truly need some serious help!!

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    dnapainter.com/tools/sharedcmv4/1845 gives you a set of possible relationships between you and your relative that shares 1845cm. I'm guessing that you can eliminate several of the possibilities (like grandparent). But half-sibling is on that list.
    – Marshall Clow
    Commented May 19, 2020 at 18:24
  • Marshall Clow, Thank you so much for your response. I’ve used that site and I truly believe the results, but I’m receiving pushback from some of my half siblings who seem to think that it’s not possible for me to be our dad’s kid so I’m just trying to get as much clarity as possible.
    – April Webb
    Commented May 19, 2020 at 23:36
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    From the numbers, it sounds like you are the girl's half-aunt, and your half-brother is her full uncle. If her dad is your half-brother's brother, that's consistent. He would only be her half-uncle if her dad was also his half-sibling. Or am I missing something?
    – cleaverkin
    Commented May 24, 2020 at 1:07
  • From what I know, the siblings only share the same dad, but not the same mom. Could that number be that high not my half brother and half niece if they share a half niece and something else relationship! Ex: like a relative on the mom’s side?
    – April Webb
    Commented May 24, 2020 at 5:23

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DNA Painter thinks that the probability of 1449 cM being a half-uncle/aunt relationship is only 5.5%. It's much more likely that he's her full uncle, meaning the following diagram accounts for all of the numbers you've given:

A---B---C
  |   |
  |  ---
  |  | |
  D  E F---G
         |
         H

Here, D is you, E is your male DNA match, and H is your female DNA match.

D-E: 1845 cM, 100.00% {Grandparent, Aunt/Uncle, Half Sibling, Niece/Nephew, Grandchild}

D-H: 949 cM, 99.65% {Great-Grandparent, Great-Aunt/Uncle, Half Aunt/Uncle, 1C, Half Niece/Nephew, Great-Niece/Nephew, Great-Grandchild}

E-H: 1449 cM, 94.49% {Grandparent, Aunt/Uncle, Half Sibling, Niece/Nephew, Grandchild}

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  • Note that there are all sorts of complications possible even in this relatively simple family diagram. For example, what if C (E's mother) has an identical twin, call her C'? If E and C' did DNA tests, then DNA Painter et alia would all claim with 100% certainty that they were parent-child. Now if B (your dad) was ...adventurous, and F's mother was C' rather than C, that would account for your information about E and F having different mothers.
    – JPmiaou
    Commented May 28, 2020 at 15:26
  • In response to the diagram, thank you so much for the visual, it definitely helps a lot! 😊 I definitely don’t think think that my 2 half brothers share the same mom for sure bc the one I matched with on AncestryDNA is 38 and his mom is 73. While my Half niece is also in her 30’s and her dad is in his 60’s. It’s all just confusing bc my dad was in his 70’s when I was born but he was married about 3 times with kids the in the age range of 77-29! It’s all very confusing.
    – April Webb
    Commented May 30, 2020 at 13:15

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