Which Is Genetically Worse?

[LexiNova]

Hi,

I'm a 19 year old biology student and my roommate, who isn't all that into science, and I were having a conversation about which would be worse (thanks to the granfather paradox which states it'd be impossible to go back in time and be your own grandfather) having a child with a grandparent or having a child with a cousin. I voted grandmother because there wasn't as much "new" DNA introduced as the cousin. I said it would be worse to because going back on your lineage is worse than going with the lineage that is equal with you. Can anyone help us sort this out because she is convinced it is the same thing.

[JackBean]

Theoretically you can have no DNA common with any of them, but grandparent is similarly related as your uncle/aunt, thus cousin is "one-generation further".

[plasmodesmata11]

he's got it, and this is a page for the coefficient of relation. It has the equation for relatedness, for future reference if you need it. and way to be thorough in trumping your roommate.
http://en.wikipedia.org/wiki/Coefficien ... lationship