Acromelanism

A cat with seal (black) point coloration.

Acromelanism or point coloration is a genetically determined, temperature-dependent pigmentation pattern, with full expression only occurring on legs, ears, tail, face and scrotum (in males). It is most recognized as the coloration of Siamese and related breeds of cat, but can be found in dogs, rabbits, rats, mice, sheep, guinea pigs, minks, and gerbils.

Locus C in Mammals

The C Locus in mammals is most often associated with the TYR gene, which controls the production of the tyrosinase enzyme that produces melanin.

In cats

"Lynx point" redirects here. For the Intel Chipset, see Lynx Point.

New-born kittens suckling milk from their seal point mother cat. Colourpoint kittens are born solid-white.

Point coloration in cats originated in the Siamese and closely related Asian breeds, and is found in many Western-developed modern breeds. It is a form of partial albinism resulting from a mutation that affects tyrosinase, an enzyme involved with melanin production. The mutated enzyme is thermolabile; it fails to work at normal body temperatures, but becomes active in cooler areas of the skin. As a result, dark pigment is limited to the coldest areas of the body, that is, the extremities. Pointed kittens are born white, since the womb is uniformly warm. As the kitten ages, the cooler areas darken while warmer areas remain cream to white in color. Points are not limited to solid colors or dark colors. It is possible to have a red (orange color) or fawn (pale warm gray) point. It is also possible to have a tortoiseshell or tabby point. A cat (of any breed) with this coloration is often called a colorpoint cat to distinguish it from others.

As the expression of the gene responsible for the pointed pattern is regulated by temperature, pointed cats who live in cooler environments often show increased darkening of their fur relative to cats who live in warmer climates, sometimes even developing large dark areas along their sides.

Because of the pigment restriction caused by the temperature sensitive tyrosinase, pointed cats' eyes are always shades of blue because the blue layer in the eye common to all cats is not covered by another color. The back of the eye also lacks pigment, giving colorpoint cats' pupils an eerie red and silver reflection in the dark, unlike a normally pigmented cat's shining silver-green or -blue.

The point gene allele is at the C locus, where pure albinism is also carried, and is written as cs. Point is recessive, so two copies of cs, one from each parent, are needed for points to be expressed. Also carried on the C locus is the gene for the sepia pattern, which allele is represented by cb. This is the darkest of all of the pigment restricting patterns—pigment is only paled at the warmest point in the body: the abdomen. Sepia cats have amber-yellow to green eyes. When a cat carries the genes cs and cb, the intermediate mink pattern is formed, in which the pigment distribution is between sepia and point. The eye color of mink cats is on the blue-green spectrum (aquamarine).

• Comparison of different black (seal, sable) colourpoint cats
• 
  Black point Siamese
• 
  Black mink Tonkinese
• 
  Black sepia Burmese
• 
  Black rosetted tabby point (lynx) Snow Bengal
• 
  Black tortoiseshell point cat

The lynx point pattern is formed by mating a colorpoint cat with a tabby cat (or breeding cats that already possess the lynx point pattern). It is characterized by a mixture of the darkening (reduced) of point coloration with distinct tabby striping on the head, tail, and legs, and an otherwise uniform and comparatively pale body. It is an accepted pattern in some cat registries, but not others, for particular breeds (mostly Siamese-related).

Point coloration is inherent to the Siamese breed and some other closely related breeds but with most other breeds the colorpoints (including lynx) were brought into some breed lines long after their establishment, but there are exceptions. For example, lynx point was a feature of some of the foundation stock of the Siberian, now called the Neva Masquerade.

Cat breeds

• Balinese
• Birman
• British Shorthair
• Burmese
• Colorpoint Shorthair
• Highlander
• Himalayan
• Javanese
• Napoleon
• Neva Masquerade
• Peterbald
• Ragamuffin
• Ragdoll
• Siamese
• Snow Bengal
• Snowshoe
• Sphynx
• Thai
• Tonkinese

In dogs

Rarely, dogs may also have a point coloration similar to that of Siamese cats.

In rabbits and rodents

Californian rabbits with point coloration

All pointed white rabbits of true breeding have red eyes. The pointed white rabbit is created with the ch gene. Its presentation is typified in the Himalayan rabbit breed (the first rabbit breed with a pointed white coat) and in the Californian breed.

Rabbit coat colors

Some rabbits that appear to be pointed white lack the red eyes, which indicates they are of different breeding. The following such coat colors are examples of those created, not with the ch gene, but with the cchl, cchd, or cchm gene in conjunction with the e gene:

• Blue point
• Chocolate point
• Lilac point
• Pearl
• Sable point
• Sallander
• Seal point
• Siamese

No pointed white rabbit can produce orange pigment; therefore, the points are always either black, blue, chocolate, or lilac. The resulting point coloration is sometimes in conjunction with a coat pattern, such as: white agouti, marten, broken, Vienna, or harlequin. (Such coats may not be recognized for showing.)

Rabbit breeds

Breeds of rabbit that include varieties with point coloration include:

• Altex
• American Fuzzy Lop
• English Angora
• French Angora
• Californian
• Cashmere Lop
• Himalayan
• Holland Lop
• Jersey Wooly
• Lionhead
• Mini Lop
• Mini Rex
• Mini Satin^{(in development)}
• Netherland Dwarf
• Pointed Beveren
• Rex
• Satin
• Satin Angora

In fancy (domestic) rats

The C - Albino locus gene causes dilution of yellow and black coloration, causing Himalayan or Siamese markings depending on the allele is affected.

Point colors in rats include:

• Sepia
• Seal Point
• Blue Point

In guinea pigs

There is only one type of guinea pig with a pointed coat. It is called the Himalayan, has either Black (a very dark brown) or Chocolate, tipped on the Ears, Nose, and Feet.

In sheep

Hampshire sheep showing point coloration of their faces, ears, and legs

Some breeds of sheep exhibit point coloration.

Sheep breeds

• Clun Forest
• Dorset Down
• Hampshire
• Norfolk Horn
• Oxford
• Shropshire
• Suffolk
• Tunis
• Valais Blacknose
• Wensleydale