Originally Posted by HDMe2
but genetically speaking I don't think it matters.
Agreed, because the incident in "Roswell That Ends Well" didn't change Fry's DNA nor that of the professor and his clone (nor, somehow, that of Fry's father, whose first name I don't remember.)
My sister has children. Her children are part her DNA and part her husband's DNA... IF I had any children, they would be part my DNA and part my wife's DNA...
Yes, so far ...
I would essentially share the same amount of DNA with my children as I would my niece or nephew... since each come from either me or my sister who are fully related to each other.
Disagreed. By calling your potential reproductive partner "wife" you've specified yourself as male; by calling your sibling "sister" you've specified her as female. Therefore you and your sister are not identical twins. Thus your DNA and hers have some differences.
Your niece and your nephew are each a 50% match to their mother, and any children you have will be a 50% match to you (treating the broken part of the Y chromosome as having the same weight as the corresponding part of the X chromosome). There is no guaranteeing what portion of her DNA matches yours, let alone what portion of the 50% of your nephew's DNA that she supplied or what portion of the 50% of your niece's DNA that she supplied you, and the same will go for her and any children you may have in the future. For one glaring example, if you ever have a son, neither his X chromosome nor his Y chromosome will match her, and thus he will certainly be less than a 50% match to your sister. (I almost said "to his aunt" but for all I know your wife may have an identical twin.)