Recently purchased SO5...great choice by me!

Question, does the breeding part of this game put more weight on choosing the sire or the mare. I read where the autopsy of Secretariat had shown this magnificent
horse had a heart that weighed in at close to 22 lbs. This large heart generated a "heart score" of 180...largest in history. There is even a book called "The X Factor" which addresses other great thourobreds
on this topic.
Anyways, all can be "googled", my point is, according to studies...the "large heart" gene is passed through the X chromosome in the mare. So.......any thoughts?
Ed