I've been studying vampirism since 1343, and I've found nothing to indicate that it has anything to do with genetics. It seems to exclusively spread through the venom/saliva of said vampires.
As for the length of my study, Steve Irwin may have taught you that in order to learn about something, you'll have to get a few bites.
Holy symbols will only effect a vampire if they followed the religion the symbol represents before they were turned. This vampire would most likely be immune, because he would have believed in Shrek, and be weak against...uh... a circle with two sticks on top?
As for the length of my study, Steve Irwin may have taught you that in order to learn about something, you'll have to get a few bites.
Would a t-posing vampire repell themselves, because they're making the image of a cross?