Using DNA and cousins to confirm or rule out great grandfather as blood.

Question

There are questions about who my grandfather's father really is.  My Grandfather is alive, but still refuses to talk about it.  Can DNA help me rule out (or confirm) his father of record without having to test my grandfather's dna?  I have connections with cousins (descendents of my grandfather's brothers and descendents of my great-great grandfather, meaning descents from his other children.)

Answer 1

Comparing your DNA results with those of your cousins will only confirm that you are related. It will not tell you who your great grandfather is.

It will help if you have a theory about who your great grandfather is, and you know someone who is for sure a descendant of that person. In that case, comparing DNA with that possible cousin will tell you whether or not you share an ancestor, and in this case if you do that would confirm your theory.

Comments

Thank you for your response.  Just to clarify.  My grandfather is one of 6 children, him being the first.  We know the identity of his mother, but there has always been a possibility that his father is different from the other 5 children.  What I'd like to do is confirm whether his father is actually his father, or not.  Does that make sense?

I have cousins that are descendents of those other 5 children, a couple of them would be willing to test.

I was also thinking another way to look at this is: I have cousins that are descendents of my Great-Great-Grandfather.  If the disconnect is my great grandfather, than really we're not cousins.  So a DNA test would say if we're related or not which would tell me whether my Great Grandfather is the disconnect that we think he might be.

Answer 2

I'm not an expert in DNA tests, but if my understanding is correct, certain DNA tests might be helpful. A Y-DNA test, which only looks at the parts enherited from the male line, might shed some information.

If the conditions are right, meaning you and the cousins that would be tested have only males in the line up to the g-grandfather, then perhaps a Y-DNA test could possibly proove a different father for your grandfather. If the Y-DNA match, it probably means the same g-grandfather or the g-grandfathers happend to have the same Y-DNA. If they differ, then a different father appeard somewhere up the line.