Curly, Wavy or Straight: The Curly Coat Gene in Dogs

Most curly coats in dogs come from variants of one gene, KRT71, which makes a structural protein in the hair. A dog with two copies of a curl variant usually has a curly coat, and a dog with one copy usually has a wavy one. Researchers have found two curl variants so far, and some curly dogs carry neither, so curl doesn't always follow the textbook.

The short version

• One main gene: KRT71, first linked to curl in Portuguese Water Dogs.
• Copies matter: one copy usually gives a wavy coat, two copies a curly one.
• Two known variants: the original curl variant is found in many breeds; a second one, found in 2019, is fixed in Curly-Coated Retrievers.
• More remain to be found: some curly dogs carry neither known variant.
• Curl traps loose hair, so curly dogs seem to shed less but need regular grooming.
• Curly isn't hypoallergenic.

The curl gene: KRT71

A study of more than 1,000 dogs from 80 breeds found that variants in three genes account for most coat types in purebred dogs, and one of them, KRT71, controls curl. The researchers mapped it in Portuguese Water Dogs, a breed that comes in curly and wavy varieties. KRT71 makes a keratin, one of the proteins that hair is built from, and variants in the same gene cause curly hair in other species too.

Curl combines with the other two coat genes. A curly, furnished, long coat gives the classic Poodle or Bichon look, while curl on a wiry, furnished coat gives the dense texture of breeds like the Airedale Terrier.

One copy, two copies

Curl is inherited as an incomplete dominant trait: one copy has a visible effect, and two copies have a stronger one. According to the UC Davis Veterinary Genetics Laboratory, dogs with one copy of a curl variant are expected to have wavy coats, dogs with two copies curly coats, and dogs with none straight coats.

This is why doodle generations differ so much. A first-generation doodle gets one curl copy from its Poodle parent and is usually wavy, while about half of F1B puppies get two copies and come out curly. Our guide to doodle generations shows the odds for each generation.

Two curl variants, and maybe more

For years, one KRT71 variant was the only known cause of curly coats in dogs. In 2019, two research groups independently found a second one. One group noticed that Curly-Coated Retrievers, a breed fixed for curly coats, didn't carry the original variant. Sequencing revealed a different KRT71 variant, also found at lower frequencies in the Lagotto Romagnolo, Bichon Frisé, Spanish Water Dog, Chesapeake Bay Retriever and Irish Terrier. The second group confirmed it was fixed in a cohort of 125 Curly-Coated Retrievers.

One curly Lagotto in the first study carried neither variant, so there are probably other curl variants still to be found. A curly dog whose DNA shows no known curl variant isn't necessarily a mystery; it may simply carry one that hasn't been described yet.

Curl and shedding

Curly and wavy coats catch loose hairs instead of dropping them, so curly dogs leave less hair around the house. The hair is still shed, though, and it builds up into mats unless it's brushed out regularly. Much of the low-shedding reputation of curly breeds also comes from the furnishings gene that often travels with curl. Our guides to furnishings and the genetics of shedding explain both.

A curly coat doesn't make a dog hypoallergenic either. A study of the main dog allergen found higher levels in the coats of so-called hypoallergenic breeds, including Poodles and Labradoodles, than in other dogs.

How a DNA report shows curl

The PuppyGenes physical appearance section includes a coat curl prediction based on KRT71, with its own confidence. In our public example reports, Juno is predicted to have a "likely wavy coat" and Marley a "likely wavy or curly coat", both at low confidence, so treat them as tentative. Our guide to long coats covers the gene that decides coat length, which also changes how curl looks.