We’ve officially wrapped up Fidome’s first deck, Coat Check, and now it’s time to get into something meatier—literally. Welcome to Form Factor, where we'll start with the breeds that are built like tanks and the genetic quirks that make them absolute units.
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If you were hoping for a single "muscle gene" that acts like a light switch, flipping dogs from lean to Hulk mode… sorry to disappoint. Genetics just isn’t that simple. No one gene is out here handing out gym memberships and whey protein subscriptions.
That said, nearly a decade ago, a study identified a cluster of genes on the X chromosome that seemed to separate the swole from the soft.
The researchers, clearly as obsessed with gains as we are, affectionately dubbed these muscle-bound dogs “Bulky Breeds.” The threshold?
Over 41kg (90 lbs) of pure, unadulterated mass.
Homozygous simply means these true freaks of nature inherit the “jacked” gene variants from both parents:
These breeds hit the genetic lottery for bulk. The mutations in IRS4, ACSL4, and IGSF1 didn’t just knock politely on their DNA’s front door; they kicked it in and set up a full-scale powerlifting gym inside.
Now, there’s another group that dipped their toes into the swole gene pool, but maybe not all the way. These mixed-bag mutants can be either homozygous (both copies of the jacked gene) or heterozygous (just one copy):
And then… the unexpected rejects—the breeds you’d think would be on the list, but somehow didn’t make the cut. That’s right, some of the most famously muscular dogs—like the Cane Corso, Great Pyrenees, Tibetan Mastiff, and Tosa Inu—got benched. No VIP access to the Bulky Breeds Club for them...At least not with this particular set of genes.
The smaller musclebound breeds—like the English Bulldog, American Staffordshire Terrier, and American Pit Bull Terrier—also didn’t get their official Jacked membership cards. Science says they’re muscular for other reasons, and we’ll get into that another day. But for now, let’s just say genetics is messy, muscles are complicated, and even the most shredded-looking dog might not have the DNA receipts to back it up.
Stay tuned for more Form Factor breakdowns because we’re only getting started.
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Because, even as an academic escapee, my inner science geek lives on.
