Kinship through potential dad's granddaughter?
So my grandfather is potentially the father of someone who contacted me. There have been rumors and speculation, but nothing is known for sure.
Could my DNA be used to find out if her dad is my grandfather?
Getting the potential father to submit to a DNA test is out of the question and it would be unlikely that his siblings or either of his children would do a DNA test.
Update:I do have a full blood brother who has the same grandpa. The other person is a girl.
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You and the other woman can both take an autosomal DNA tests. They cost about $99. You might want to test your brother as well. Yes, you should be able to determine if the three of you are closely related using what is called triangulation - or comparing the genetic makeup of the three of you.
The reason I suggested also testing your brother is because we inherit about 50% of our genes from each parent, and ABOUT 25% from each grandparent. That means you and your brother could each inherit a different 25% or it could overlap. Think of it as the DNA lottery. Since the woman has about 50% of your grandfather's genes, there is a better chance of getting a close match if both of you are tested. I would suggest either 23andMe or FamilyTreeDNA because both are highly regarded and offer the needed chromosome matching tools. I believe 23andMe offers a discount on more than one test.
If you have questions about interpreting the tests, this group may be of help:
http://groups.yahoo.com/group/DNAAdoption/
It can be fairly easy if this is your paternal grandfather and you have a full brother and if your grandfather is also the father or paternal grandfather or the person contacting you and that person is a male.
If so your grandfather, your brother and that person would share the same Y DNA.
Otherwise it is not so simple. Most of your DNA is Autosomal. You get it 50-50 from both parents but not necessarily 25% from each of your 4 grandparents. The reason why when your parents passed on the Autosomal they received from their parents to you it was randomly jumbled and went through a process of recombination. Therefore what you inherited can be biased between grandmother and grandfather on both sides of the family. How you inherited any bias will not be how your siblings inherited it. Now some companies will take your autosomal and match you with individuals in their database going back 5-8 generations. So if they can do that they might be able to take the both of your Autosomal and see if there is a relationship. Contact some of these companies, 23andme, FamilyTreeDNA etc. With FamilyTreeDNA all you have to do is go under Feedback at the top on their website and there is a way you can email them and ask questions.
You are asking a PATERNITY question, which would be better asked in a medical category.
I do know that DNA testing would reveal if you could be related.