As far as I know, this theory has already been refuted and it was stated that those DNA strings are used for portraits only.
Correct. Congenital traits are inherited based on a pure percentage chance defined in crusader kings ii\common\traits\00_traits.txt (or another trait file in the same location) and looks like this:
Code:
birth = 50
inherit_chance = 25
Where the first is how many children in 1.000 are born with the trait spontaneously and the latter being the percentage chance of it being inherited.
There's also
Code:
agnatic = yes