[Everything] A question on the amount of DNA two main characters share.

I know this a fictional fantasy world, so it doesn't really matter, but I'm curious about how much DNA Jon & Dany would share in the real world.

We know Jon is Daenerys' nephew, and normally aunt and nephew share 25%, but with all the inbreeding Targs in their bloodline, how much does that change things?

Rhaegar & Daenerys were brother and sister, their parents were also brother and sister and so were their grandparents. Before that there were a few generations of people marrying into other families, so I'm not sure if that kind of resets the whole inbreeding thing, but going back to Aegon the Conqueror it seems that more Targs in the royal line married their relatives than married out into other families.

If we hypothesize that Jon got 50% of his DNA from Lyanna and 50% from Rhaegar, how related is he to Dany?