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Family Finder and siblingship

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  • Family Finder and siblingship

    I'm posting my response to this discussion to a new thread since it doesn't belong in the other thread. I'm sure this thread will get locked eventually, but let's at least set the record straight before it does

    Originally posted by JohnLloydScharf
    The one who should READ their email is Max. Here is what I sent him:
    Regarding Family Finder for discrimination between half sibling and a cousin
    John, read your own email. Your subject said half, but in the body of your message, you did NOT say half:

    Originally posted by JohnLloydScharf
    Hide Details
    John Scharf
    Max Blankfeld BBA FTDNA VP Operations/Marketing
    Message flagged Monday, July 11, 2011 1:32 PM
    Message body
    Here is a question for you. Can Family Finder discriminate between a sibling and a cousin?

    OBVIOUSLY, he cannot read and responded with:
    Yes, definitely, and proven by records of individuals that we have tested. A siblingship relationship has a lot more centimorgans in common than a cousin relationship
    Max answered the question that you asked in the body of your email. Don't expect him to be a mind-reader and know that you MEANT to ask about a half-sibling instead.

    Originally posted by JohnLloydScharf

    I am sorry, but you did not respond to the question I asked. Please read what was written because this is a very specific question. I did not say a siblingship. I said a half-sibling. They share one parent and not another. Are you saying Family Finder cannot discriminate between brothers and half brothers?

    Are you saying my half-brother would look like a brother?
    Cousins share one set of grandparents and not another.
    Half brothers share one set of grandparents and not another.

    I have a cousin whose mother was the identical twin sister of my mother. We share one set of grandparents and not the other. Would he and my half brother look like they are my full brothers?

    Family Finder can absolutely discriminate between brothers and half brothers.
    Your situation of a cousin that is a son of an identical twin sister cannot be generalized for the purpose of your question, because this is a very specific situation

    OBVIOUSLY he cannot read, AGAIN. The QUESTION is if Family Finder can discriminate between a half-sibling and a first cousin. Both Max and you should be ashamed of how you are misrepresenting this test.
    No, what is shameful is that you keep twisting the question around. In the original thread where this discussion began two weeks ago, you insisted that FF could not be used to determine siblingship at all. Then you insisted that FF can not discriminate between siblings and cousins in general, then you specified half-siblings and second cousins. Now you're asking about half-siblings and 1st cousins, and even more specifically, half-siblings and 1st cousins whose mothers are twins! Each time we respond, you twist the question and then call us liars. Nice, real nice.

    I think anyone else reading this will have no trouble seeing who's being shameful here.

    But let's have some fun and address each of these scenarios that you've asked about:

    Siblings (full or half) vs 2nd cousins and further: YES, FF can differentiate

    Full siblings vs half Siblings: YES, FF can differentiate

    Half siblings vs 1st cousins (non-twin parents): Maybe. Half-siblings share 25% of their DNA on average, while 1st cousins share 12.5% of their DNA on average. This should be enough to differentiate them, but due to the random nature of inheritance, people could share more or less than average, making it slightly more challenging to differentiate between these two relationships.

    Half-siblings vs 1st cousins from one set of twin parents: No, FF can not differentiate between the two. Twins have the exact same DNA, so it would be just like one parent having children from two different spouses -- ie, half siblings.

    Full Siblings vs 1st cousins from two sets of twin parents: No, FF can not differentiate between the two. Again, the twins each share the same DNA, so this would be just like one set of parents having children.


    Do you think the traditional siblingship test, which you seem to hold in the highest regard and think can give us ALL the answers, can differentiate between ALL of these scenarios?

    No. The same thing would happen in the twin scenarios with traditional siblingship tests as with FF. And for non-twin scenarios, if you don't have a parent's DNA to compare as well, traditional siblingship tests cannot always provide conclusive results either, especially when we're talking about half siblings.

    So why are you not scrutinizing traditional siblingship tests as well?

    But let's get back to the bottom line again...

    The original question was simply: which test can determine if two men are half brothers vs unrelated? We advised that Y-DNA can confirm if they're related on the direct paternal line and that FF can determine if they share enough DNA to be half-siblings. That answer still stands, end of story.