There are various mutations affecting the tail and in 1940 American zoologist Ida Mellen wrote of oddities in cats' tails including kinked, bobbed, curled and even double tails. Curly tailed cats were known in China in the 12th Century (probably bobtails) and ringtail cats were known in the USA sometime prior to 1940. In 1868, Darwin wrote in The Variation of Animals and Plants Under Domestication "Thropughout an immense area, namely the Malayan archipelago, Siam, Pegu, and Burmah, all the cats have truncated tails about half the proper length, often with a sort of knot at the end."

The bobtail trait ranges from a normal-length tail with a distinct kink, through to a short twisted pom-pom and just about anything between those two extremes. The degree of kink is variable and the vertebrae are affected so that the tail cannot be straightened. It is often possible to feel a bony knot inside the kink where vertebrae have fused. The bobtail mutation(s) is widespread throughout Asia, extending as far as Russia. It is well know that early Siamese cats had kinked full-length tails and this is still seen in Siamese-type cats in Thailand, but has been bred out of pedigree Siamese cats. According to folklore, colourpointed cats were kept by Thai royalty and one legend has it that a princess entrusted her rings to a palace cat while she bathed. She threaded them on the cat's tail and the cat knotted its tail so the rings did not fall off. The kink therefore marks where it knotted its tail - a charming tale, but acquired traits are not passed on in this way. Unlike the Manx mutation, there appear to be no detrimental effects of the bobtailed mutations.

"Tailless" cats have occurred periodically around the world through random mutation. They have been reported in Bosnia, Burma, China, Crimea, Java, Malaya, Denmark, Nova Scotia and Thailand though some of these will have been bobtails. Bobtail cats occur throughout Asia and into Russia, with more recent mutations occurring in the USA. In a 1949 study, the geneticist A.G. Searle found no kinked tails in London cats. He studied Singapore's cats in 1959 and eventually concluded that stubby-tailed cats were common in Singapore, but in general were rare in Europe except for the Manx breed where the tail was often completely absent. The Manx and the Asian bobtails are due to different mutations, though this would not be established until later.

More recent research indicates that the tailless gene (T) has 4 alleles i.e. there are four different versions of the same gene. The Manx breed is based on one of those mutations, and that mutation can have side effects such as spina bifida. The PixieBob and American Bobtail are also based on mutations of the same gene. However, the Kurilian Bobtail is due to an incomplete dominant gene, while the similarly named Karelian s bobbed tail is due to a recessive gene. In the Japanese Bobtail, the gene itself is autosomal dominant, however, homozygous cats have the desired bobtailed trait therefore breeders treat the gene as though it were recessive. Although the bobtailed mutation in American Bobtails and Pixie-Bobs was believed to be unrelated to the mutation found in the Manx, recent DNA analysis has found some shared alleles (Multiple mutant T alleles cause haploinsufficiency of Brachyury and short tails in Manx cats, Buckingham, K.J., McMillin, M.J., Brassil, M.M. et al. Mamm Genome (2013) 24: 400.).

The authors of the "Brachyury and short tails" study noted that five cat breeds were known to have abnormal tail length phenotypes: the American Bobtail, the Manx, the Pixie-Bob, the Kurilian Bobtail, and the Japanese Bobtail (the Karelian, Toy-Bob and short-tailed Chausies were not surveyed). They sequenced the T (tailless) gene in several unrelated lineages of Manx cats from both the USA and the Isle of Man, where the cats originated, and identified three 1-bp deletions (three separate deletions of base pairs from the DNA) and one duplication/deletion. Each of these could cause a frameshift resulting in a malformed Brachyury protein. Grossly simplified, the genetic code is read three base pairs at a time, so deleting or inserting a base pair means the following triplets are read out of phase and incorrectly translated.

Ninety-five percent of Manx cats with short-tail phenotypes were found to be heterozygous for T mutations, the exact mutant allele seeming to be specific to a particular lineage. This means that Manxes have different combinations of mutant T alleles present, which explains the variability in tail length from completely missing through to almost full length - in that breed. One of the mutant T alleles found in the Manx was also found in American Bobtails and Pixie-Bobs. The Pixie-Bob also has a tail-shortening gene from a Chausie that was incorporated as a foundation cat (see note). The findings indicate that the mutant Brachyury protein is one of the mechanism causing variable tail length in domestic cats. Further short-tailed alleles may have been introduced into the domestic cat gene pool from serval hybrids (Savannahs) and caracal hybrids (Caracats).

Note: After TICA initially recognized the PixieBob there was an open registry and similar-looking cats of American Bobtail, Japanese Bobtail and Manx ancestry are likely to have been registered as foundation cats for the PixieBob breed. TICA also permitted "Legend Cats" (naturally occurring bobtails that resembled bobcats) to be registered as PixieBobs. Spotted Chausie variants also appear to have been registered as Legend Cats, and a Jungle Cat hybrid called El Gato del Oro became a prize-winning Pixie-Bob.

The bobtailed mutations are not related to the Manx mutation. They have occurred independently in various geographic areas and are widespread in Asia and parts of Russia. An Abyssinian Bobtail has been reported in non-pedigree Abyssinian-type cats (location not specified). A Spanish bobtail has also been reported. Cats with knotted, shortened, kinked and pom-pom tails are relatively common in Tenerife and the Canary Islands, the mutation apparently having become established due to the isolation of the gene pool, and tourists frequently mistake the trait for breakage. Similar mutation have occurred spontaneously in the USA. Over the years there have been purported Bobcat hybrids that have inherited the short tail from the wild parent, but none have held up to genetic scrutiny. According to leading feline geneticists, the genes governing tail conformation are located on a mutation hotspot.

According to an earlir anatomist, Sir Richard Owen, and to Professor H N Moseley, the kink in the Siamese's tail (a mild form of the bobtailed trait) was the relic of a prehensile tail, possibly inherited from civet ancestors (though neither civets nor genets had prehensile tails)! Others asserted that the kink was due to intercrossing the Siamese with the "common strain" however Lilian J Veley wrote in 1926 that this could be discounted since there was no other cat known in Siam, "common" or otherwise that had ever possessed an original kink, making it a folly to try to eradicate the trait. Presumably Ms Veley had not encountered the numerous bobtailed and kink-tailed street cats in Thailand. In "Our Cats" of May 1901 there was information on the Siamese's tail from interviews with the King of Siam and his Private Secretary. While the cats in the Royal Palace apparently had no kinks in their tails, occasionally a "tramp cat of Malay origin" strayed in and the resultant crossbred cats had kinked tails.

In 1783, Willian Marsden, Fellow of the Royal Society and late Secretary to the President and Council of Fort Marlborough wrote in "The History of Sumatra" of the Malay Cat: "All their tails imperfect and knobbed at the end." In 'The Variation of Animals and Plants under Domestication", Darwin wrote "throughout an immense area, namely, the Malayan Archipelago, Siam, Pequan, and Burmah, all the cats have truncated tails about half the proper length, often with a sort of knob at the end. [ ] The Madagascar cat is said to have a twisted tail." Another writer and traveller, Mivart, had corroborated the statement regarding the Malay cat, of which he said the tail "is only half the ordinary length, and often contorted into a sort of knot, so that it cannot be straightened [ ] Its contortion is due to deformity of the bones of the tail". Joseph Train had also mentioned th Malayan cats, comparing them with the Manx: "The Manks rumpy resembles some what in appearance the cats said by Sir Stamford Raffles to be peculiar to the Malayan Archipelago." Sir Stamford Raffles' name is closely associated with Singapore.

HC Brooke reported seeing three spotted tabby Malay cats in Holland in the 1880s and some very similar specimens at the Jardin d'Acclimatation in Paris around the same time. "The tails of these [Paris] cats, about three or four inches long, were tightly screwed, or at least the tail formed three complete revolutions. The 'screw' tail, as also the spotted type of colouration, appear to be becoming very rare." In 1889, Mr O Gould had apparently taken four Siamese to Ceylon and soon Ceylon was "overspread" with their progeny, known as "Gould's Cats" and many had kinked tails in spite of there being no Malay cats for them to interbreed with. Lilian J Veley wondered if the Malay cat's kink had come from the Siamese rather than the other way round (she considered the Siamese to be the older type). She also implicated the Korat "a blue variant of the Siamese, to which our 'blue-pointed' freaks are due."

German writer Jean Bungartz described several bobtailed cats in his 1896 book "Die Hauskatze, ihre Rassen und Variet ten" (Housecats, Their Races and Varieties) in "Illustriertes Katzenbuch" (An Illustrated Book of Cats). He noted that according to Brehm Martens, on the Sunda Isles and in Japan there were cats with different lengths of tail. Kessel had told Weinland that there were short-tailed cats on Sumatra. Bungartz added that the cats of Cochinchina had only a short, curled tail and the Madagascar cat had a turned, knotted tail.

R Shelford, former Curator of the Sarawak Museum wrote in his book "A Naturalist in Borneo" "It may be mentioned here that the domestic cat of the Malays is quite a distinct variety [...] it is a very small tabby with large ears and a body and hind-legs so long that it lacks all grace. The tail is either an absurd twisted knot or else very short and terminating in a knob; this knotting of the tail is caused by a natural dislocation of the vertebrae so that they join onto each other at all sorts of angles." The length of hind-leg was a trait shared by the Manx, leading some cat-fanciers to believe that the two were related.

Miss Lowndes, daughter of the novelist Mrs Belloc Lowndes described a Malay kitten that she had acquired. It had recently arrived, along with its mother, from the Straits Settlements. "It has a triple-kinked tail. It is, unfortunately, not of the spotted kind, but these seem to be very rare nowadays." More information was provided by Mr Boden Kloss, Director of the Raffles Museum and Library at Singapore "The tail which distinguishes these cats may be clubbed or kinked, very short or of medium length, and the animals themselves of many colours - plain, piebald, or patterned." He also wrote "A fair proportion of the cats of Singapore seen in native villages are short-tailed animals with a kinked tail. There would [be], I should say, three or four kinks. In colour they may be tabby, or boldly black and white. As a point of interest it may be noted that Felis planiceps [Flat-Headed Cat], one of the wild species of the peninsula, tends to resemble the domestic Malay cat in the matter of tail." The cat writer HC Brooke, who had an interest in the Malay cat, wrote that F planiceps and the domestic cat were unlikely to be inter-fertile.

Mr H O Forbes had exhibited a bobtailed Malay cat to the Liverpool Biological Society and shown the cause of the knotting to be the development of wedge-shaped cartilages between the tail vertebrae. Forbes attempted to link the Malay bobtails to the bobtailed cats found in part of Portugal. In the 1920s, Forbes wrote "My remarks referred to the interest I had in exhibiting the creature's skin from the occurrence in the East of what I had noted as extremely common in the cats of Portugal when I lived there about 1876. The kink, I was told was then believed to have become hereditary, from a custom long practised by the Portuguese of pinching or breaking the tails of the new-born kittens, and it would be of special interest if it could be established that the kink in the Malayan cats' tails had been communicated to them through those imported by the early Portuguese into the East. If I can trust my memory the tail of this cat, though short and kinked had the full number of vertebrae, some of them reduced and wedge shaped." Others disputed his theory as the trait had been reported in the Malay cat since at least 1783 and no amount of tail-pinching would cause the trait to become hereditary!

The Madura or Buso cats are a closed colony of bobtailed blue cats with green eyes which live on the tiny and isolated island of Ra'as off the coast of the Indonesian island of Madura (it is a 6 hour ferry ride from Madura to Ra'as). There are reckoned to be less than 100 of these cats and they are in danger of extinction, in part due to local beliefs that prevent the exportation of fertile cats. The Madura breed and its decline have been documented by Dr Ronny Rachman Noor (Faculty of Animal Science, Bogor Agricultural Universtity). The cats are known to the islanders as "Kucing Buso" (grey cat) and the true Madura cat is blue self, suggesting they may have come from Korat stock taken to the island on trading ships. There is some mythology surrounding the breed, just as there was about the "Royal Siamese". The true Madura cat, originating from Ra'as, may only be kept by high-ranking people such as religious leaders, high rank government officials and informal leaders. Anyone attempting to smuggle a cat from Ra'as will find their boat sinking. The cats' posture and the triangular facial shape are similar to the wild cat and leopard. The cats are large with a medium length tail with a visible bend or kink at the end. The fur is relatively thick. The true Madura cat is solid grey known as "buso" often with lavender nose leather. A few so-called Madura cats on Madura can be found with the brown sepia, mink and colourpoint patterns as well as blue bicolours due to matings with local cats. A brown mink "Madura cat" exhibited at a cat show in Surabaya was of Japanese Bobtail type. The declining numbers appear due to people trying to export the cat out of the island and to a high mortality rate among breeding cats, both on Ra'as and on Madura, indicating either a lethal gene or a high degree of inbreeding. Cats brought out from Ra'as are castrated due a local belief that the fertile Buso cat may only be kept at the Ra'as island (castration in itself may pose dangers of infection). To preserve this cat as a distinct type and avoid extinction, breeders would need to establish breeding lines which would mean obtaining unneutered cats. The restriction on who may own a true Madura cat also limits ownership and controlled breeding.

There are various tales associated with the Asian bobtailed cats. The Siamese tail kink, for example, was supposedly due to a princess threading her rings on the cats' tails for safekeeping and the loyal cats kinked their tails to keep the rings in place. Siamese were also believed to be royal palace cats. Likewise Madura cats may only be owned by people of high status. A Malaysian belief is that if a kittens tail is cut off and buried under the doorstep, the cat will not stray from home. Another is that monks cut the tails off of cats so that the cats do not go to heaven. A cat with a stumpy tail is not perfect and imperfect creatures cannot go to heaven. I examined a tabby cat brought back from Japan whose owner claimed that its tail had been cut off by monks during kittenhood. I found evidence of knots and kinks in the remnant of tail which told me it was a natural bobtail. Also, the tail ended quite normally in a black tip. This was a perfectly normal genetic bobtail, though the owner preferred to think she had rescued an abused cat.

In 1988, the Cat Association of Britain finalised the standard for the "Oriental Bobtail"; a cat of oriental (or foreign) conformation and coat, but with a bobbed tail. Since then, little or nothing has been heard of this breed. Another British bobtail, the Anglesey Bobtail was mentioned as a new/experimental variety in 1996.

The most famous bobtailed breed is the Japanese Bobtail found in both shorthair and semi-longhair varieties. This is due to a recessive gene. Cats are not indigenous to Japan, but reached the islands along Asian trade routes hundreds of years ago. It has appeared in ancient Japanese art and has evidently existed back as far as the 6th century. It is claimed that it was introduced into Japan from China at that time, which corresponds to Ida Mellen's account of curly tailed cats in China. Once the pet of Japanese nobles (according to folklore), it eventually spread to the general population but was not considered anything more than a common moggy. It attracted the interest of American breeders in 1968 and was recognised in the US in 1978. The longhaired version had always existed (longhair is due to a recessive gene) but was not given breed status until 1991.

In a study comparing the genetics of several breeds (Lipinski MJ, et al., The ascent of cat breeds: genetic evaluations of breeds and worldwide random-bred populations, Genomics (2007), the Japanese Bobtail was found to be more closely related to Western cats than to Asian cats, though the breed showed some Asian genetic influence. The Japanese Bobtail was imported into the USA in 1968 and developed as a breed in the USA. As a result, the gene pool of the exhibition Japanese Bobtail was largely influenced by European/American cats rather than by Asian cats. The Japanese Bobtail (theexhibition version developed in the USA) is distinguished by its bobtail and high-cheekboned triangular face. Close-lying, silky short hair. The tail is 10-13 cm in length if fully extended, but due to the kinked structure it appears only 4-7 cm long. The tail hair often grows straight out in all directions, giving it a rabbit-like fluff-ball or pom-pom appearance. In Japan, bobtails are found in all colours including agouti (Abyssinian pattern) and colourpoint though these are not accepted in the Western fancy.

In 2001 a Singapura Bobtail was reported in a breeding programme. The bobtail kitten appeared in a Singapura litter, tracing back to a part-tailed foundation cat. Inbreeding can cause recessive genes to reappear. The kitten initially appeared to be tailless, but proved to have a stumpy tail similar to that of the Japanese Bobtail. This is not surprising since there are numerous bobtails in Singapore.