If Y DNA is passed from father to son and mtDNA from mother to daughter then how do you show relation to grandparents?

Question

If Y DNA is passed from father to son and mtDNA from mother to daughter then how do you show relation to grandmothers and grandfathers? The problem is that I have traced my lineage from grandparents to grandparents back through time. I have practically nothing on my dad’s side, but my mother’s side goes all the way. And where a trail ends I pick up from the other great grandparent, that grandparent could be male or female. How do I use DNA test to show a relation in this case if it is strictly male line or female line?

Answer 1

First - a clarification. Y-DNA is passed only from father to son, but mtDNA is passed from mother to son or daughter.

Secondly - because Y-DNA and mDNA only follow the direct paternal and maternal lines, the answer to your question is that you can't use these types of tests to confirm relationships in the scenario you're describing. You could, however, potentially use autosomal testing, if these relationships are fairly recent (within ~8 generations).

Answer 2

Your YDNA and mtDNA are only a small portion of the DNA that makes you, you. We each receive about 25% of our genetic material -- auDNA -- from our four grandparents. You are still 25% your maternal grandpa even though you do not carry his YDNA or his mtDNA.

(I want to clarify this as I've seen repeatedly on G2G that folks do not understand how DNA inheritance works. Someone was posting passionately about how if one's maternal grandfather was a full-blooded Native American, then one would "have no Indian blood" since we don't inherit our maternal grandfather's YDNA or mtDNA. But in this scenario one would still be 25% Native American, via autosomal DNA inherited from your numbered chromosomes. Your maternal grandfather's DNA does not magically disappear because you don't inherit your sex chromosomes from him).

Answer 3

Y DNA is really helpful for eliminating potential male ancestors. If it matches one person in your grandfather's generation it will also match all of his male siblings. It will also match his father and his father's male siblings and their descendants, etc. This can be a very large pool. It does allow putting people in a pool that you can then do a paper trail on so it can help, but it won't solve your problem in any automatic way.