Is this horse physically capable of the career I want to ride him in? This is the easier of the three qualities to assess right out of the gate, because looking at the competitive careers of the dam, sire, and siblings of your young horse can reflect alot in terms of potential. Ability has varying inheritance; studies have shown jumping is a fairly directly inheritable trait (about as directly inheritable as it gets, at any rate), whereas movement is not. Instead, movement most likely has a strong environmental component, with the foals copying the movement of the mares around them.
To add an extra layer, some genes are “sex-linked”, which is to say they are passed along through the “X” in the gender-specific “XY” and “XX”. So for a colt or a gelding, that “X” is inherited from mom – not dad – making her perhaps a more important component between the two. One of these genes is the “X-factor” gene, or big heart gene. It has been studied extensively in racehorses, and is linked to large increases in athletic ability. It was, in fact, likely a large reason Secretariat so far outpaced all the other horses in the field. And remember – he inherited this from his dam, not his sire! In addition, mDNA (mitochondrial DNA) is only provided from the mare to her offspring. It is largely unknown what effects this mDNA has on the horse’s athletic performance, but it is known to effect cell respiration and efficiency. This means it is worth taking a closer look at your horse’s mareline, the mares in his pedigree in general, and any sires of the mares in your horse’s pedigree. We will go into greater detail of marelines and this sort of inheritance in a later discussion.