Shared DNA

[darkerhorse]

Since a granddaughter inherits 25% of her DNA from a given grandparent, can we say that they "share" 25% of their DNA, suggesting that the "shared" DNA also makes up 25% of the grandparent's DNA?

Also, I don't suppose we can say that a grandniece inherits DNA from a grand-uncle, but can we say that they share a given percentage of DNA? If so, what is that percentage?

While I'm at it, is it grand-uncle or granduncle?

[MarcuccioV]

Well, first of all, there is a slight fallacy in your example. DNA is ONLY inherited equally from parents -- after that it gets muddy. There are possible instances where a grandchild might not receive ANY DNA from a specific grandparent due to random replication (ie: a GC might get approx 1/3 from 3 GP's, and 0 from the 4th. Rare, but possible. Or the percentages can be completely uneven, favoring one parents side more than the other. Again, this is rare, but possible. On average, 25% is close but not completely accurate. This is one reason why siblings DNA varies so much (they each get differing percentages from each grandparent). A better way to explain this is that each child gets differing portions of the 50% of each parent's DNA (with some overlap, of course). So a particular child will get DNA from a 50% of a parent's DNA that are not equal between the parent's parents.

So when you get further removed (grandniece grandnephew/granduncle grandaunt) it gets even more unbalanced. There are online charts that explain DNA based on possible relationships. But there will always be a range because of the element of random recombination.

And it is "granduncle" (same as grandparent or grandchild)...

[darkerhorse]

Thanks for your explanation. What about the term "shared"? Shared means they both have it, but does 25% shared really mean it constitutes 25% of the DNA of each?

I thought granduncle was correct, but it doesn't look as fluid, as say grandfather. I've read that many compound words were once hyphenated and maybe even separated before that. For instance, it might originally have been "grand uncle", and then with common usage it becomes "grand-uncle" as if they've met and are now going steady, and then finally they marry and become one - granduncle.

[darkerhorse]

Can these DNA tests estimate how much DNA you've inherited from each grandparent? Would it require a DNA test for your grandparent too? If so, would a DNA test for a parent help? In my case, there's no one from either generation alive, but I'm curious for others sake.

[MarcuccioV]

Can these DNA tests estimate how much DNA you've inherited from each grandparent? Would it require a DNA test for your grandparent too? If so, would a DNA test for a parent help? In my case, there's no one from either generation alive, but I'm curious for others sake.

Yes, it would require DNA tests by the grandparents. For parents, some tests (such as Ancestry) use a technology that separates parents by splitting the chromosomes to see what ethnicities are inherited from each parent. It is up to you to then decide which parent is which (in cases such as ours, where the parents are from different cultures, that is easy, if both parents are of similar ethnicities, I suppose that might be difficult).

In some cases, if many family members test (in my case, on my maternal side, there are very, very few), you can get a better idea on relationships by looking at what Ancestry calls "shared matches". There are also "clusters" which group matches together based on who they match with.

Since you haven't tested (yet), it's impossible to check these factors. Hopefully, if or when you do, your matches will be more evenly distributed between your parents than mine are. My stats currently sit at 29,585 paternal matches vs 705 maternal. Even my (legitimate) first cousin, whose mother is Sicilian, has almost an equally unbalanced distribution. I can only hope you would (will) have better luck than I have had...