I don't know, amethyst. I think it was genius of Stephanie Meyer to include the genetics side of the matter in the book. To me, a person who absolutely loves fantasy novels, it was a good idea to do this. That way, she could make this story more realistic, instead of simply a story, it becomes believable. It shows how science is involved with life - even in storybooks. And it also goes to show that Edward and Carlisle (not to mention all of the other characters) have a reason to worry about a loved one's health and why they worry about it, even as "indestructible" vampires. How could Meyer include an explanation of the problem without mentioning the potential cause of the problem - the chromosomes?
And anyway, Edward wouldn't be Edward if he didn't consider all of the possibilities behind why Nessie is the way she is.
And I don't know much about biology either, but look at how the heart starts beating faster during the conversion from human to vampire. Maybe an enzyme from the venom that causes this phenomenon also causes Nessie's accelerated heartbeat. Also the higher body heat might be explained by this theory. Theoretically, if this enzyme was present at the time of Nessie's development in the womb, wouldn't her body try to make up for this difference? Then it would be written into her DNA for her to have a higher heart rate and temperature.
But, I agree that a link between Nessie and the werewolves if pretty questionable. But Edward and Carlisle only ever theorized about such a connection. They never actually proved that it really existed.
And finally, authors include interesting things like this so that we "deep thinkers" have more to ponder over, ergo more time thinking about the book. In the end, look out! We are obsessed with trying to solve the mysteries of the book. And by the time we realize that we're obsessed, it's too late to escape
