Polydactyly in Maine Coons: The ‘Pd’ Gene Explained#

[cite_start]A normal cat has 18 toes: five on each front paw, and four on each back paw[cite: 1277]. A Polydactyl Maine Coon can have 20, 24, or even 28 toes. They look like they are wearing mittens, or snowshoes.

For years, these “Hemingway Cats” were looked down upon by the show world as “mutants.” But historically, they are a core part of the Maine Coon breed. [cite_start]In fact, some estimates suggest that 40% of the original population of Maine Coons were polydactyls[cite: 1521].

Here is the genetics behind the “Thumb Cat.”

The Genetics: A Simple Dominant#

[cite_start]Polydactyly is caused by the autosomal dominant gene Pd[cite: 3119].

• Dominant: This means you only need one polydactyl parent to get polydactyl kittens. It cannot “hide” or skip a generation. [cite_start]If a cat has normal feet, it does not carry the gene[cite: 2946].
• Variable Expression: The gene turns the “extra toe” switch on, but how many toes you get is variable. You might get a small dewclaw or a massive “patty paw” with 7 toes. [cite_start]The hind feet are rarely affected unless the front feet are also affected[cite: 2945].

Is it a Defect?#

There is a myth that polydactyly causes “Radial Hypoplasia” (twisted limbs).

• The Truth: There are two different genes. [cite_start]The gene found in Maine Coons ($Pd$) is generally harmless and causes no structural defects other than the extra digits[cite: 2944].
• [cite_start]The Other Gene: A different gene ($Rh$) found in the “Twisty Cat” mutation does cause crippling forearm deformities[cite: 3131]. This is NOT the gene found in the Maine Coon gene pool.

Historical Context: The Sailor’s Luck#

Why were there so many Polys in Maine? Sailors prized them. The Maine Coon Cat by Liza Gardner Walsh notes that polydactyls were considered “good luck” on ships. [cite_start]Their massive paws gave them better balance on heaving decks and made them superior rat catchers[cite: 1282]. [cite_start]The “Boston influence” helped spread this mutation up the coast to Maine[cite: 1521].

The Show Hall Controversy#

Here is the split:

• TICA (The International Cat Association): Accepts Polydactyl Maine Coons for Championship status. They judge the cat on its structure, regardless of toe count.
• [cite_start]CFA (Cat Fanciers’ Association): Still considers polydactyly a disqualification in the Maine Coon[cite: 1645]. However, many CFA breeders still secretly use Polys in their breeding programs (to get heavy boning) and pet out the Poly kittens.

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Conclusion#

Polydactyly is not a disease; it is a charm. It is a harmless, dominant mutation that harkens back to the breed’s working roots on the ships of New England. If you have a Poly, you have a piece of living history.

References#

1. Vella, C. et al. (1999). Robinson’s Genetics for Cat Breeders and Veterinarians. “Polydactyly,” p. [cite_start]201. [cite: 2945]
2. Walsh, L.G. (2013). The Maine Coon Cat. “Physical Characteristics,” p. [cite_start]13. [cite: 1276]
3. Danforth, C.H. (1947). “Heredity of polydactyly in the cat.” Journal of Heredity.
4. TICA. Maine Coon Breed Standard: Polydactyl Division.
5. Chapman, V.A. (1961). “The anatomy of polydactylism in cats.” [cite_start]Anatomical Record. [cite: 3119]
6. Lloyd, A.T. (1986). “Pussycat, pussycat, where have you been?” Natural History.