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    23 and Me DNA test

    My brother got one of those 23 and Me DNA tests. If I got the same test, would I be able to tell if we have the same biological father? The thing is: My sister looks like my dad. I look like I'm half my dad and half my mom. But my brother only looks like my mom. Makes me wonder.

    But would the test tell anything about paternity?

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    Re: 23 and Me DNA test

    Quote Originally Posted by Stretch View Post
    My brother got one of those 23 and Me DNA tests. If I got the same test, would I be able to tell if we have the same biological father? The thing is: My sister looks like my dad. I look like I'm half my dad and half my mom. But my brother only looks like my mom. Makes me wonder.

    But would the test tell anything about paternity?
    They should tell everything, but only if all parties are willing to submit to testing.
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    Re: 23 and Me DNA test

    Quote Originally Posted by Stretch View Post
    But would the test tell anything about paternity?
    Yes, it can show paternity, it depends. But, I'm going to give you a better answer than that, an answer I might have needed when I was at your point of asking.

    If I can offer what I know from using ancestry.com, the relationship between any two people is evaluated by the number of centimorgans the two people share. A centimorgan is a unit used to measure genetic linkage. The two people would have to each submit their DNA to the same site for this evaluation. Your dad would have to provide his DNA then each sibling who also provided their DNA would be compared to not only him but to each other, and to really anybody else who had ever submitted their DNA to the site. A list is provided (not shown in this post), showing the people who share significant quantities of centimorgans, from highest to lowest, from all the poeple who have submitted to that site. Then, they tell you what types of familial relationships share each quantity of centimorgans on the list.

    For example, I have no full-siblings but several half-siblings. One of my half-brothers and I submitted our DNA to the site. We already know we have different fathers and neither is alive to provide his saliva for their test. My brother showed up on my Match list in second place, sharing 1,398 cM. The site then provided this list of possible DNA relationships for that quantity of centimorgans:



    Since we already know we are half-siblings, we can find that relationship on the list. We know we are not any of the others one there! So, the site told us that we do NOT share the same two parents. What it didn't (or can't) tell us is which parent we have in common, mother or father. But, we already know, as we grew up with each other. We share a mother. BTW, take notice how they percentaged things out.

    We can use the above example to help us with the next example where we didn't grow up with each other and had only overlapping family stories.

    Through other means than DNA, I encountered a half-sibling whom I never knew existed. It was from me posting info on genealogy websites, seeking anybody to contact me who recognized my story. Based on shared family stories, it appeared we shared the same father but different mothers. I had not yet joined the website at this point but he had, so when I joined and my Match list was provided me, he showed up in first place with 1,773 centimorgans, more than my other half-brother. For that higher quantity of centimorgans, there is 100% probability that we are half-siblings. However, as before, they don't say whether we share a father or a mother. But, our overlapping family stories inform us that we share a father.




    Don't ask me why a shared mother showed fewer shared centimorgans than a shared father. I don't understand it all yet.

    If I had a full-sibling, I bet the two of us would show up with a boatload of common centimorgans and the accompanying list of possible DNA relationships would include "full sibling" at 100%. That would clearly mean you and your sibling shared paternity and maternity.

    However, if you're results with your sibling were like mine, that would mean that you shared only one parent, either mother or father. In this situation, it is not telling you paternity. You'd need outside info to know which parent you share.

    In both examples, we established only the genetic connection. Without parents participating, the site could not say whether we shared father or mother.

    But, you specifically asked about paternity. For that, you'd need your dad to submit his DNA for each sibling to be compared to him. That's why I first said it depends. It depends on whether your dad is alive and willing to provide his saliva. Even then, it wouldn't actually state paternity, only the probabilities.

    Perhaps 23andMe works the same way, as DNA is DNA.

    Hope this helps. It's been rewarding for me.
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    Re: 23 and Me DNA test

    My dad is alive, but asking for his DNA might come across as weird. My brother has already done his 23 and Me test. If I do the exact same test and compare it to his, will that be enough to know if we share paternity? We know we both had to have come from the same mother. She's the one who went to the hospital all big and pregnant. So if the test showed 100 percent, then we must be both the same paternity and maternity, but if it's only 50%, then it's half. Right?

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    Re: 23 and Me DNA test

    Quote Originally Posted by Stretch View Post
    My dad is alive, but asking for his DNA might come across as weird. My brother has already done his 23 and Me test. If I do the exact same test and compare it to his, will that be enough to know if we share paternity? We know we both had to have come from the same mother. She's the one who went to the hospital all big and pregnant.
    I know this is a lot to absorb and, if you are like I was, you already had it in your mind that it would be explained differently. Be prepared to dump from your brain any prior beliefs about how this works.

    Like I said, it will only show possibilities of the relationship between you and your brother, not paternity. If your brother shows up on your match list, it will say one of these two things:

    1) You have the possibility of full-sibling with him. Which means you can deduce paternity in that you have the same father (and mother).
    2) You have the possibility of half-sibling with him. You'll have to come up with your own way of figuring out which parent you share.

    If your brother does NOT show up on your Match list at all (nor do you show up on his), then that says this to you about that:

    3) You have (the possibility of) no relationship to him. Which means that you have entirely different parents than your brother. Surprise! One of you two is adopted!


    Quote Originally Posted by Stretch View Post
    So if the test showed 100 percent, then we must be both the same paternity and maternity, but if it's only 50%, then it's half. Right?
    That's not quite how I meant the percentages I showed. They are not going to say you're 50% of your dad. They don't know he is your dad (and they don't care). He's just another saliva sample to them. He's just another registered username. They are only going to say how many centimorgans you share with that registered member of their site and then list the percentages of possible DNA relationships you may actually have with that member. It will be YOU who will know that registered member is your dad and it will be YOU who will have to view that accompanying list of possible DNA relationships and decide which relationship on that list is most likely applicable to you and that member (dad).

    Bottom line, people whom you know are submitting their DNA will either show up on your Match list or they won't. If they do, then you have to pick from their possibilities list what relationship you think that person is to you (and that's where you need to bring outside information to bear). If they don't show up on the list, that mean's you ain't related to them. On ancestry.com, you will not get the info any better than what I have described here.

    My guess is that you may see either of two results for your Dad on your Match list:

    1) If he is your biological dad, he's on your match list and probably at the very top as your closest relative, and the accompanying list of possible DNA relationships would include "parent-child" or similar, and probably at 100% possibility. So, they are NOT saying that 50% of you is that member. Do you see what I am saying?

    2) If he is NOT your biological dad, he's not even going to show up on your Match list at all, unless, hehe, he shows up on page 57 as a 4th cousin thrice removed, and then you will have to wonder about THAT! LOL.

    Does that explain it any better? 23andMe may have their own presentation format. Perhaps your brother can tell you what his Match list looks like for that site. He likely has one, even if his top matches thus far are only, say, distant cousins.

    You don't have to approach your dad like you are doubting paternity. Many if not most people use these websites to trace ancestors for genealogy's sake as it is very interesting. Your dad's DNA contribution is invaluable for this and will help you and your family explore your roots going back to Europe or wherever your ancestors hailed from.

    Get him interested in the genealogy aspect of this and get yourself interested, too. I wish my parents were alive to have contributed. I know my step-dad would have loved to see his proud heritage as explained by DNA. My mother was supposed to be full-blooded but you find out that even that was an assumption made in the days before DNA. Turns out, she had small percentage of other nationalities. So, I can no longer say I am half-blooded of what she is.
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    Re: 23 and Me DNA test

    Quote Originally Posted by Stretch View Post
    My brother got one of those 23 and Me DNA tests. If I got the same test, would I be able to tell if we have the same biological father? The thing is: My sister looks like my dad. I look like I'm half my dad and half my mom. But my brother only looks like my mom. Makes me wonder.

    But would the test tell anything about paternity?
    My only previous experience of DNA testing was when a friend had it done for a paternity case and they talked about Alleles.

    I hadn’t heard of Centimorgans before, interesting. I tried researching it a bit but to be honest it’s all a bit above my head.

    However, on my travels I came upon this that may explain things a bit:

    https://now.tufts.edu/articles/pulli...ancestry-tests

    I hope it helps.


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