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Family Finder Advanced Topics Advanced discussion about Family Tree DNA's Family Finder Product.

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  #1  
Old 14th November 2017, 05:49 PM
BedfontLass BedfontLass is offline
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Half Sibling - How to prove?

I am a female. I believe I have found my half sister, ie same father different mother. If she agrees to take the FTDNA Family Finder test, which I have already done so, what results (data numbers) would prove this to be correct? Would this DNA test be the best one to take?

Last edited by BedfontLass; 14th November 2017 at 05:51 PM.
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Old 14th November 2017, 06:09 PM
MoberlyDrake MoberlyDrake is offline
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Yes, she should do the Family Finder, which will be able to tell if you are half-siblings. The Holiday sale has started and there are coupons issued weekly, but different ones to different people. You may be able to find someone who has a Family Finder coupon code they aren't going to use themselves.
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  #3  
Old 14th November 2017, 07:39 PM
marietta marietta is offline
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This chart giving cMs for relationships should be helpful.
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Old 14th November 2017, 08:53 PM
prairielad prairielad is online now
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Sisters with the same father will also match the entire length of X (approx 196cM on X at FTDNA)

Matching entire X does not automatically mean shared father, but strengthens case . (ie Aunt/niece will show same autosomal amount as half sibling, and can also show full x matching)
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Old 15th November 2017, 10:43 AM
John McCoy John McCoy is offline
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When the Family Finder results come back, you can upload both DNA files to the free GEDmatch web site. The GEDmatch "One-to-One" comparison tool has a "graphics option" that will display both the half-identical as well as the fully-identical chromosome segments. Half-siblings will have at most a few VERY SMALL fully-identical segments (assuming there are no additional relationships among the parents), because they share only one parent. Full siblings will have MANY VERY LONG fully-identical segments because they share both parents. The difference is very obvious.

FTDNA's matching statistics count all matching segments as if they were only half-identical, a fact that reduces total matching cM for full siblings and makes the distinction between half-siblings and full siblings less obvious.

For the future, it would be a really useful improvement if FTDNA could add (as a separate total) the count for fully-identical segments to its matching statistics. This may sound complicated, but actually it simplifies the interpretation of the results.
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Old 15th November 2017, 12:31 PM
MoberlyDrake MoberlyDrake is offline
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And you could offer to pay for and/or manage the test yourself. If you pay for the test yourself,you can have all email sent to you. You have to share the password with her, but she can't change the password or prevent you from accessing the results unless she reimburses you. Even if she pays for and manages her own kit, she will appear on your results page, provided she is really your sister and doesn't make her results private.
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  #7  
Old 15th November 2017, 09:01 PM
Germanica Germanica is offline
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Quote:
Originally Posted by John McCoy View Post
When the Family Finder results come back, you can upload both DNA files to the free GEDmatch web site. The GEDmatch "One-to-One" comparison tool has a "graphics option" that will display both the half-identical as well as the fully-identical chromosome segments. Half-siblings will have at most a few VERY SMALL fully-identical segments (assuming there are no additional relationships among the parents), because they share only one parent. Full siblings will have MANY VERY LONG fully-identical segments because they share both parents. The difference is very obvious.
That's true, but I don't think this is a question of half vs full siblings. It sounds like the two people in question are relative strangers, so it would more be a question of whether they are half siblings, or some other, more distant relation.

BedfontLass, when you get the results in, pop the total amount of DNA shared into here: https://dnapainter.com/tools/sharedcm and it will list possible relationships.
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Old 15th November 2017, 10:54 PM
dna dna is online now
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Quote:
Originally Posted by Germanica View Post
That's true, but I don't think this is a question of half vs full siblings. It sounds like the two people in question are relative strangers, so it would more be a question of whether they are half siblings, or some other, more distant relation.

BedfontLass, when you get the results in, pop the total amount of DNA shared into here: https://dnapainter.com/tools/sharedcm and it will list possible relationships.
That is an extremely useful tool!


Mr. W
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  #9  
Old 16th November 2017, 05:47 AM
marietta marietta is offline
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Germanica: Yes, thank you! The variance of shared cMs is astounding, especially that you could share up to 2108 cMs with a GREAT niece/nephew.
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