Ow…my head…I loved my animal breeding class, but I just got caught up in all of the old information that I can’t remember and ow…
anyway, assuming a common ancestor of the great-great-great-great-great grandparent, the cousins would be twelve degrees removed, so the consanguinity would be (1/2)^12, which would end up being around 0.0244% of the DNA
(seriously, if you want to learn more, read all of those links…then take an animal breeding course. none of the messy “ethics” and “cultural sensitivity” that’s found in human genealogy courses)
The thing is, unless you have a complete pedigree of a person, you really can’t figure the F-values that far out, since there’s likely been crossing of distant relatives at some point or another in the direct lineage. It’s sometimes not even possible to genetically determine that people are fourth cousins, and farther out, it’s almost impossible to tell.
You know, in the end 99.5% of our DNA is identical. You probably shouldn’t have a baby with your first cousin, cause there’s about a 2.5% chance above the baseline for serious congenital defects without genetic counseling. My head hurts now. Go learn stuff and find answers if I didn’t understand your question.