The Curl Gene Explained: Why Some Dogs Mat and Others Don't
Chapter 02 · Coat Science
The Curl Gene Explained: Why Some Dogs Mat and Others Don’t
Three genes decide coat length, curl and furnishings. Knowing which ones your dog carries explains the brushing routine better than the breed name does.
“It’s just a curly-coated breed” isn’t really an explanation — it’s a label for something that has an actual mechanism. Coat length, curl, and the mustache-and-eyebrows look some dogs have (and others don’t) are governed by three specific genes, identified in a widely-cited 2009 study (Cadieu et al., Science) that sequenced coat variation across hundreds of dog breeds. Knowing what each one does explains why your dog’s coat behaves the way it does, and why brushing advice that works for one hair-coated dog can be wrong for another.
FGF5 — the length switch
FGF5 controls whether hair keeps growing or stops at a fixed length. Dogs with the short-coat variant grow hair to a set length and stop, the way most fur-type breeds do. Dogs with the long-coat variant don’t get that stop signal — hair keeps growing, which is why hair-type breeds need trims rather than relying on natural shedding to manage length. It takes two copies of the long-coat variant for the long-hair trait to show.
KRT71 — the curl dial
This is the gene our Coat Profile quiz asks about, and it’s the one that matters most for matting. KRT71 doesn’t work as a simple on/off switch — it behaves more like a dial:
N/N
Zero copies
Straight coat
Shed hair falls or brushes out with little resistance.
N/Cu
One copy
Wavy coat
The curl shows up, but loosely — hair still releases fairly easily.
Cu/Cu
Two copies
Tight, springy curls
Curl catches loose hair, coils it into the coat and holds it there.
A dog with a Cu/Cu genotype has a coat that curls back on itself far more than a wavy N/Cu coat, and that structural difference is exactly why it traps loose hair instead of releasing it. Straight and wavy coats let shed hair fall or brush out relatively easily. A tight curl catches it, coils it into the surrounding hair, and holds it there — which is the actual reason Cu/Cu dogs need more frequent, more deliberate brushing than N/Cu dogs of the same breed.
It’s not that their owners are less diligent. It’s a structural property of the coat.
RSPO2 — furnishings, and why some dogs have “no face”
RSPO2 controls what breeders call furnishings: the longer hair that forms a mustache, eyebrows, and beard on breeds like Schnauzers, some Poodles, and wire-coated terriers. A dog with the long-coat and curl variants but without the furnishings variant ends up with what’s called an “improper coat” — a coat that’s long and possibly curly, but missing the facial furnishings typical of the breed. It’s a real, documented genetic combination, not a grooming mistake, and it’s one reason two dogs of the same breed can look noticeably different around the face.
Cording — what happens when a tight curl coat is left unbrushed
Take a Cu/Cu coat and stop brushing it, and the same catching mechanism that causes small mats keeps compounding: adjacent mats merge into longer rope-like sections, a process called cording. It’s the same underlying structure that breeds like the Puli and Komondor are deliberately groomed into as a breed standard — the difference is intention and maintenance, not a different coat type. For a Poodle, Doodle, or Bichon, cording is what unmanaged matting turns into over time, not a style choice, which is the practical reason regular brushing matters more for Cu/Cu coats than for any other genotype.
What this actually means for your dog
Genotype, not just breed, determines how much brushing your dog’s coat needs. Two Labradoodles can have completely different maintenance needs depending on whether they inherited one or two copies of the curl variant — breed alone can’t tell you that. That’s the gap our Coat Profile quiz is built to close: it identifies genotype from a few quick questions and gives you a brushing and bathing routine matched to the actual coat, not just the breed name on paper.