The gene(s) for polydactyly specifically affects the tissue formed at the very end of the limb (apical cap) of a developing embryo. This is the area where the toes will form. If the apical cap is larger than normal, extra toes will develop from it. It is worth noting that physical damage to the apical cap might also trigger the development of extra toes. Branching of the apical cap will lead to complete double paws or, if it branches early enough, to doubled limbs.

   In 1955, Albert C Jude, author of "Cat Genetics" (a book that had as much about mice and rabbits than cats!) documented two forms of polydactyly. He wrote that polydactylism (extra digits), and oligodactylism (reduction of toe number) were sometimes reported by the fancy, but were the exception (not selected for) rather than the rule within cat breeding. This meant little data was available on feline polydactyly to permit proper scientific study. He noted that polydactyly involving only the preaxial side of the limb had been documented in cats by Danforth in 1947 and was dominant over the normal form. Most cases of polydactylism in cats observed by Jude had affected the front feet only!!! Neat, huh?

   Jude also described another form of polydactyly, the type we now call "mitten cats" but which he called "posterior reduplication", in his 1955 book: Another interesting deformity - only very occasionally seen in cats, but more frequently seen in some other animals - is known as "posterior reduplication." The condition was found in a stock of mice by Danforth in 1923, and a description was published by him in 1930. This deformity is mentioned here mainly to show how information of a helpful nature can be given by fanciers. In this instance it came from Mrs. A. Winsor of Hull, a well-known English Abyssinian breeder. Before the war, says Mrs. Winsor, "I had two little black she-cats. One came into season, and a strange gray tom came to investigate. His feet were really amazing. His front legs were very thick and stout, big feet, with normal number of toes. On the inner side of each foot was another smaller foot. A sort of stalk grew from the ankle, as if the ankle bone had been split, and this ended in a complete foot which rested on the ground alongside the normal foot, and turned slightly inward. When sitting he had to advance one leg, as he could not possibly put all his four feet side by side, and when walking he sort of lifted one foot over the other. He mated my queen who was calling at the time and there were two black kittens whom we put to sleep, and two gray-striped, both females. One had just thumbs; the other had seven toes - four ordinary, and three extra where the thumb would be. There was no stalk, but these three toes had a separate pad; they were about the same length as the others, and her feet spread out like paws. She also had a sort of "thumb" half-way up each hind foot, with a claw on the end. The other gray-striped female - the one that had just thumbs - we kept for eight years and then she died. I managed to get a granddaughter who is now seven years old. She has bad countless kittens, and about half of every lifter have the ‘Family Feet.’"

   It is interesting that Jude differentiated between the 2 types of polydactyly in 1955; differentiating between the two forms has recently become a concern for cat breeders due to the occurrence of Twisty Cats, or RH cats.

    According to the late Roy Robinson in his book "Genetics for Cat Breeders", polydactyly has been officially (scientifically) recorded as early as 1868, though it had been observed earlier and seen frequently since. The distinguishing feature is the presence of extra toes, most noticeably on the front feet. Robinson explains that there is considerable variation in the number of extra toes and in how well-formed they are. The trait ranges from an enlargement of the inside digit into a "thumb" to the formation of three apparently well formed extra toes (i.e. 7 toes on the affected foot). A cat may even have different numbers of toes on each of its front feet.