Where does incest end?

I never could have imagined to post something with this title, but here's my question:

My character has an awesome aunt (high stats, attractive and strong) who is almost the same age as him. Besides she is just his half-aunt because she's the half-sister of his father (same father, different mother). She has that little blood symbol by her portrait which shows she's of the same dynasty. Does the game recognize that their genes probably differ more than those of normal family members or is there the same probability of inbred children for same family marriages?