The was an episode, "The Doctor's Daughter", where the doctor's dna was used to make a young female clone of him. He could get in some incest action. Actually, he already has (David Tennant, who played the Doctor, wound up marrying Georgia Moffett, who played the daughter, and they now have three kids)
On top of that, Georgia Moffett is the daughter of the guy who played the Fifth Doctor (Peter Davison, né Moffett).