As you’ve no doubt noticed by now if you’ve been subscribing to this blog for any length of time, we’re big fans of Murmur Farm’s Maryland stallion Blofeld. As such, we track his progeny quite closely, and we had noticed that what seemed to be a disproportionate amount of his black-type winners share Blofeld’s gray/roan coat color. So, as the mating planning season winds down, we thought we’d do a little bit of a deeper dive into the numbers to see if that impression actually stands up to scrutiny.
(*Please note, before we get going, we aren’t mathematicians or statisticians — though we did take a couple of stats courses in undergrad while earning a BA in English. But this post is designed to be fun and hopefully interesting, rather than to intended to show anything with statistical significance.)
First, a quick genetics lesson for Thoroughbreds, which come in four recognized colors: bay, gray/roan, chestnut and dark bay/brown. If you remember your Punnett squares from high school biology, chestnut is a recessive gene, and bay is dominant (for this purpose, we’re going to lump bay and dark bay/brown together, as we haven’t ever heard the genetic distinction between those two colors — and frankly, it happens often enough that you see a horse that’s bay listed as dark bay/brown, and vice versa, to feel like maybe nobody is totally sure how different they are, if at all).
So, if you have a chestnut parent, you know that side of the Punnett square is “bb” with two recessive genes. And thus, two chestnut parents can only produce a chestnut foal. A bay (or dark bay/brown) parent can either be “BB” or “Bb”. The former would be what we call a “true breeding bay”, meaning it can only have bay offspring. (War Front and Into Mischief are both true breeding bays and cannot have chestnut foals.) A horse with the “Bb” combination could pass either of those genes onto a foal, and thus could produce either a chestnut or bay/brown foal, depending on what the other parent contributes.
Now, the gray/roan gene is a mutation, and a gray/roan parent either passes that gene onto its offspring or not. If it does, the offspring is also gray/roan (regardless of the underlying Punnett square-dictated outcome), and if it doesn’t, the offspring is not — so there’s a 50/50 chance that the product of a gray/roan parent will also be gray/roan (unless both parents are gray/roan, then there’s a 75% chance the foal will be gray/roan). A gray/roan foal must have at least one gray/roan parent.
OK, so Blofeld is a gray/roan stallion. That means you’d expect about half of his foals to get that gray/roan gene from him, and thus to be gray/roan also. And from his 149 named foals that are 3YO or older, he has 74 registered as gray/roan, which is 50% (if we round). Blofeld has 36 bay foals (24%), 25 dark bay/brown foals (17%), and 14 chestnut foals (9%) (which means that underneath his gray/roan mutation, Blofeld is a “Bb”).
His runners and winners track these percentages pretty closely: 54 gray/roan runners (50% of all his runners), 42 gray/roan winners (49% of all his winners), 28 bay runners (26%) with 22 winners (26%), 16 dark bay/brown runners (15%) with 12 winners (14%), and 10 chestnut runners (9%) with 9 chestnut winners (11%).
Looking at Blofeld’s 20 black-type runners (10 each, winners and placed), we find that 10 are gray/roan (again, 50%), 3 are bay (15%), 3 are dark bay/brown (15%), and 4 are chestnut (20%) — so the chestnuts are overachieving a bit in black-type company, and the bays are underachieving, relative to the percentage of foals that have those colors.
Here’s where it gets really interesting, though. If we look just at Blofeld’s 10 black-type winners, he has 1 each that are bay, dark bay/brown, and chestnut, but 7 (SEVEN!) that are gray/roan. That means fully 70% of his black-type winners are gray/roan, rather than something close to 50%. And his bay or dark bay/brown runners underperform (10% each, rather than something close to 25% and 15%, respectively). His one chestnut black-type winner tracks from his 9% chestnut foals overall.
What does this mean? Probably nothing, really. But it’s a good reason to root for more of our Blofeld foals to be gray/roan (or at least chestnut), beyond the fact that we just find those colors more pleasing to look at, anyway.
