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I am trying to determine who my biological grandparent was.

I am female, I found a genetic female second cousin. We are both DNA tested on 23andme, along with my brother. My brother also had a Y-test on Ancestry. All results uploaded to Gedmatch. I know that one of my second female cousin's aunts or uncles (her parent) is my grandparent but which one. I share X with her, my brother does not. His ancestry y-test on Gedmatch does not. Through Ancestry Y-test I found a male relative of my second cousin's mother's family. I had it confirmed by Ancestry that only paternal line would show as genetic relative. I believe that one of my female second cousin's uncle is my paternal grandfather.

Am I on the correct track?

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    Hi cathy, welcome to Genealogy & Family History SE! You can take the tour to get an overview of how the site works. I've made a couple of minor edits to your question. If you are able to add a bit more detail about the lengths of the DNA matches then you might be able to get a more detailed answer that is specific to your case. You can add information to your question using the edit button below your post.
    – Harry V. ♦
    Jan 28, 2017 at 19:08
  • My father's parents were not his biological parents, To keep things simple I will refer to them as his mother and father. I found through DNA testing that I am closely related to his mother's side. I found a estimated 2nd cousin, 4.72% shared 20 segments (23andMe) Gedmatch largest segment 44.8 cM, total segments 7cM=359.5cM, MCRA 2.7 generations.
    – cathy
    Jan 29, 2017 at 21:52
  • Add on: Cousin is niece of my father's mother.
    – cathy
    Jan 29, 2017 at 21:53
  • Add on: a estimated 4th to 6th male cousin was found on Ancestry, my brother Y-test. This cousin is also member of my father's mother's side. His grandmother is first cousin once removed of my father's mother. Another male 5th cousin on that same side of family, only proven on Gedmatch when tested against my brother's Ancestry Y-test on Gedmatch.
    – cathy
    Jan 29, 2017 at 21:53
  • I just found out that Ancestry was an autosomal test not a Y-test
    – cathy
    Jan 30, 2017 at 19:46

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Based on the information you have provided, I don’t think you are quite on the right track. You state that:

I believe that one of my female second cousin's uncle is my paternal grandfather.

However, you could not inherit any X-DNA from your paternal grandfather. All of your X-DNA comes from your paternal grandmother and maternal grandparents. You inherited an X-chromosome from each of your parents (red and green on the diagram below). The red X came from your father, which came from his mother. The green X came from your mother.

enter image description here

You can see from this diagram that you cannot have inherited an X from your paternal grandfather, because he only passed on a Y to your father.

Based on the information given, you could be related to your supposed second cousin on either your paternal grandmother or maternal grandparents' lines:

enter image description here

The fact that your brother shares no X-DNA with the second cousin makes it perhaps more likely that you are related through your paternal grandmother, since your brother inherited no X-DNA from her, while you did. It is equally possible that he just inherited a different X-chromosome segment from your mother, and that you are related to your second cousin via your mother. It is very difficult to say anything more specific without the particulars.

My final comment is on the fact that you keep referring to your DNA match as a "second cousin". The relationships you describe in your question ("second female cousin's aunts or uncles is my grandparent") would actually make her your first cousin once removed. You do not state the length of the match, but keep in mind that there is very wide range of match length for a second cousin (43-504 cM (average 238 cM) according to the Shared cM Project). Therefore, keep in mind that you might not actually be second cousins, you could (for instance) be related less closely and happen to share more DNA than average for your degree of relationship.

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