Board Thread:Manga Discussion/@comment-27399549-20151214184558/@comment-1739368-20151214200856

It may be hereditary to some extent, but I think there's too many determinants for the vampire part to have transfered over. We know Jonathan's body unlocked the other Joestar's stands, each of Dio's kin have the joestar birthmark, and Giorno's hair wasn't originally blonde. Seems to suggest to me, the joestar gene is the dominant one. However, this may have been because these children were conceived well before the events of Part 3, back when Dio had less control over Jonathan's body.