Genetic mutations are important sources of variability among individuals of all species, including cats. While these genetic anomalies can have different impacts—beneficial, neutral or even harmful—their occurrence is very important as it provides the populations with diverse and unique individuals. This furthermore increases the chances of survival of at least one fraction of the population in case of sudden environmental changes.

Some of these anomalies can result in differences in the aspect of physical appearance. In the wild, mutations that lead to the unusual appearance of cats would normally fail to breed in great numbers and they would often quickly disappear from the populations. However, in domestic cats some of these body-type mutations (i.e. folded ears) are considered attractive by humans which led to human selection and perpetuation of them. This is not always good for our pets, as many of these naturally occurring mutations are actually harmful (or even lethal when in homozygous form) and would normally be removed from the population if there weren’t for human intervention.

Take a look at some of the mutations identified to be associated with unusual appearances of our favorite pets.

Variations in ear shapes

Typically, cats have erect and slightly pointed ears. There are several identified mutations though that can impact the form and shape of feline ears.

1.Folded ears: this trait is associated with the “Scottish Fold gene” Fd. This anomaly is a natural dominant-gene mutation characteristic for the Scottish Fold cat breed. Their ears are folded forward and down to different degrees of folding. However, this gene is also associated with cartilage defects such as swollen feet and thickened tail. The mutation is harmful in homozygous form (FdFd) in which case it causes osteochondrodysplasia. This is why breeders breed folds only with non-folds to avoid homozygous folds.

2.Curled ears: this unusual trait is associated with the “American Curl gene” Cu. This is a typical characteristic of the American Curl cat breed. Fortunately, no harmful defects associated with this gene have not been identified. However, ears of these cats need to be handled carefully as the ear cartilage can be easily hurt. Regular ear cleaning is also required because more of the inner ear is exposed in comparison to typical ear forms.

3. Rounded ears: are a trait observed in a cat in Italy and some free-roaming cats in Texas. These ears are rounded rather than pointed in shape. While the carriers of the trait in Texas died out, the one found in Italy is being assessed for breed potential.

4. Four ears: are associated with a recessive mutation that results in four ear flaps (additional flaps do not lead to additional organs of hearing). Sometimes due to duplicate ears, eyes may be reduced in size and the jaw slightly undershot. According to the studies from 1957* the carriers of this trait are relatively inactive and lethargic and may struggle with possible interferences of the brain functioning. This mutation also seems to be lethal with most kitten carriers typically dying in utero. Despite historical data, most recently reported four eared cats have been healthy indicating that there may be more genes involved in the unusual ear configurations.

*Little, C. C. (March–April 1957). “Four-Ears, a Recessive Mutation in the Cat”. Journal of Heredity. XLVIII (2): 57.

Variations in tail appearances

1.Japanese bobtail: this is an unusual characteristic of a “bobbed” tail observed in the Japanese Bobtail cat breed. The trait is associated with an autosomal dominant mutation of the Japanese bobtail gene Jb. This means that both homozygous and heterozygous for this gene will have bobbed tails. Unlike other unusual tail shapes, the mutation causing for bobtail’s tail is harmless and does not relate to lethality or skeletal disorders.

2. Manx tailless: this is a trait caused by a harmful dominant mutation in the Manx tailless gene M. Homozygous carriers (MM) die before birth while heterozygous carriers (Mm) are either tailless or have very short, stumpy tails. Sometimes they can also exhibit skeletal and organ defects, with some Manx cats dying before ever reaching 12 months of age.

3. Short tails: tails short in length can be very difficult to distinguish from bobbed or Manx tails. Shortened tails can occur in many different pure or mixed breeds and can be caused by different genetic mutations—of which, most are still being investigated.

4. Curly tails: tails looping over from the back come in different forms and can be caused by different mutations. One such mutation have been developed into the new experimental breed called American Ringtail. The breed started with a Californian cat named Solomon in 1998. The mutation identified in this cat doesn’t seem to be associated with any health issues. The curly-tailed cats were bred with Ragdolls and American Shorthairs.

Variations in paws

1. Syndactylism: this is a trait associated with the Split Foot gene Sh. The dominant mutation of the gene causes the reduction of the number of toes, giving the so called “lobster-claw” appearance.

2. Polydactylism: this is a trait associated with different dominant and recessive genes causing for a higher number of toes than normal. To learn more about this unusual appearance read our blog about polydactylism here.

Variations in height and size

1. Munchkin legs: this is the trait of shortened legs and it is caused by a dominant mutation in the Munchkin gene Mk. Homozygous (MkMk) carriers may be at a higher risk of dying as the kittens are very small in the litter. However, the mutation doesn’t seem to be causing impaired mobility or spinal problems and the Munchkin cats are not disabled despite having short legs. The anomaly is not achondroplasia, but can be either hypochondroplasia or pseudoachondroplasia (meaning that the long bones of the legs are affected and other bodily proportions remain unaffected).

2.Teacup sized Persians: are very small, diminutive but proportional Persian cats whose size is caused by a dominant germ-cell mutation first identified in a male Persian Treker in 1995. Today the Teacup Persians are a separate breed and not all of them are descended from Treker. Most of these kittens today were actually raised from Silver and Golden color divisions.

Variations in coat colors and patterns

Cat coats come in diverse patterns and colors. To learn more about peculiar genetics of feline coats please read about Cat coat genetics (part 1) and Cat coat genetics (part 2).

Types of mutated cat breeds

Most mutations associated with certain unusual appearances are breed specific as humans targeted these traits when breeding their cats. Here is a list of some of the better known mutation cat breeds recognized in various cat associations (list by