I agree with all the other posts.... Tatum is such a laid back Yorkie that sometimes I wonder if she's "not normal"!
I do sincerely believe it's the environment that any dog is raised in that form their personalities. We had a toy poodle for 15 years that was also extremely laid back. He always surprised people that had the preconceived notion that all poodles are yippy. Be firm and consistent with your training and I think you'll raise a loving dog. Of course, as is the such with kids, they can also have their own definite personalities no matter what you do so good luck!