Cat coat genetics

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A tabby mother and her kittens, showing different colorations Charline the cat and her kittens.jpg
A tabby mother and her kittens, showing different colorations

Cat coat genetics determine the coloration, pattern, length, and texture of feline fur. The variations among cat coats are physical properties and should not be confused with cat breeds. A cat may display the coat of a certain breed without actually being that breed. For example, a Neva Masquerade (Siberian colorpoint) could wear point coloration, the stereotypical coat of a Siamese.

Contents

Solid colors

Eumelanin and phaeomelanin

Eumelanin

The browning gene B/b/bl codes for TYRP1 ( Q4VNX8 ), an enzyme involved in the metabolic pathway for eumelanin pigment production. Its dominant form, B, will produce black eumelanin. It has two recessive variants, b (chocolate) and bl (cinnamon), with bl being recessive to both B and b. [1] Chocolate is a rich dark brown color, and is referred to as chestnut in some breeds. Cinnamon is a light brown which may be reddish.

Sex-linked red

Basic colors
Red Cat in Torzhok City.jpg
A male red tabby showing the XOY-genotype
Tortoiseshellshorthair (2013 photo; cropped 2022).JPG
A female black tortoiseshell cat showing the XOXo-genotype

The sex-linked red "Orange" locus, O/o, determines whether a cat will produce eumelanin. In cats with orange fur, phaeomelanin (red pigment) completely replaces eumelanin (black or brown pigment). [2] This gene is located on the X chromosome. The orange allele is O, and non-orange is o. Males can typically only be orange or non-orange due to only having one X chromosome. Since females have two X chromosomes, they have two alleles of this gene. OO results in orange fur, oo results in fur without any orange (black, brown, etc.), and Oo results in a tortoiseshell cat, in which some parts of the fur are orange and others areas non-orange. [3] One in three thousand tortoiseshell cats are male, making the combination possible but rare- however, due to the nature of their genetics, male tortoiseshells often exhibit chromosomal abnormalities. [4] In one study, less than a third of male calicos had a simple XXY Klinefelter's karyotype, slightly more than a third were complicated XXY mosaics, and about a third had no XXY component at all. [4]

Diluted colors
Dilute orange tabby cat.jpg
A cream (diluted red) tabby cat
Dilute tortoiseshell cat 2.jpg
A blue (diluted black) tortoiseshell cat

The pelt color commonly referred to as "orange" is scientifically known as red. Other common names include yellow, ginger, and marmalade. Red show cats have a deep orange color, but it can also present as a yellow or light ginger color. Unidentified "rufousing polygenes" are theorized to be the reason for this variance. Orange is epistatic to nonagouti, so all red cats are tabbies. "Solid" red show cats are usually low contrast ticked tabbies. [5]

The precise identity of the gene at the Orange locus is unknown. It has been narrowed down to a 3.5 Mb stretch on the X chromosome in 2009. [5]

Dilution

The Dense pigment gene, D/d, codes for melanophilin (MLPH; A0SJ36 ), a protein involved in the transportation and deposition of pigment into a growing hair. [5] When a cat has two of the recessive d alleles (Maltese dilution), black fur becomes "blue" (appearing gray), chocolate fur becomes "lilac" (appearing light, almost grayish brown-lavender), cinnamon fur becomes "fawn", and red fur becomes "cream". [6] Similar to red cats, all cream cats are tabbies. The d allele is a single-base deletion that truncates the protein. If the cat has d/d genes, the coat is diluted. If the genes are D/D or D/d, the coat will be unaffected. [5]

Overview of dilutions in cat coat colors [6]
Basic colorDilutionDilute modifier, double dilution
Black ("brown")Blue ("gray")Caramel, blue-based caramel (UK)
ChocolateLilacTaupe, lilac-based caramel (UK)
CinnamonFawnFawn-based caramel (UK)
Red ("orange")CreamApricot
AmberLight amberUnknown
WhiteN/AN/A
Two amber tabby Norwegian Forest cats, showing the colour difference with age. On the left a female kitten, on the right a male adult. Ginny en Apollo.jpg
Two amber tabby Norwegian Forest cats, showing the colour difference with age. On the left a female kitten, on the right a male adult.

Other genes

Tabbies

A mackerel tabby with the classic "M" on forehead CAT2007 05 16.jpg
A mackerel tabby with the classic "M" on forehead

Tabby cats have a range of variegated and blotched coats, consisting of a dark pattern on a lighter background. This variety is derived from the interplay of multiple genes and resulting phenotypes. Most tabbies feature thin dark markings on the face, including the 'M' on the forehead and an eyeliner effect, pigmented lips and paws, and a pink nose outlined in darker pigment.[ citation needed ] However, the following different coat patterns are all possible:[ citation needed ]

Agouti

Agouti hair showing alternating bands along the shaft Poil agouti.svg
Agouti hair showing alternating bands along the shaft

The agouti factor determines the "background" of the tabby coat, which consists of hairs that are banded with dark eumelanin and lighter phaeomelanin along the length of the hair shaft. The Agouti gene, with its dominant A allele and recessive a allele, controls the coding for agouti signaling protein (ASIP; Q865F0 ). The wild-type dominant A causes the banding and thus an overall lightening effect on the hair, while the recessive non-agouti or "hypermelanistic" allele a does not initiate this shift in the pigmentation pathway. As a result, homozygous aa have pigment production throughout the entire growth cycle of the hair and therefore along its full length. [10] These homozygotes are solidly dark throughout, which obscures the appearance of the characteristic dark tabby markings—sometimes a suggestion of the underlying pattern, called "ghost striping", can be seen, especially in bright slanted light on kittens and on the legs, tail and sometimes elsewhere on adults.

A major exception to the solid masking of the tabby pattern exists, as the O allele of the O/o locus is epistatic over the aa genotype. That is, in red or cream colored cats, tabby marking is displayed regardless of the genotype at the agouti locus. However, some red and most cream tabbies do have a fainter pattern when lacking an agouti allele, indicating that the aa genotype does still have a faint effect even if it does not induce complete masking. The mechanism of this process is unknown.

Dark markings

The Tabby locus on chromosome A1 accounts for most tabby patterns seen in domestic cats, including those patterns seen in most breeds. The dominant allele TaM produces mackerel tabbies, and the recessive Tab produce classic (sometimes referred to as blotched) tabbies. [11] The gene responsible for this differential patterning has been identified as transmembrane aminopeptidase Q ( Taqpep , M3XFH7 ).[ citation needed ] A threonine to asparagine substitution at residue 139 (T139N) in this protein is responsible for producing the tabby phenotype in domestic cats. In cheetahs, a base pair insertion into exon 20 of the protein replaces the 16 C-terminal residues with 109 new ones (N977Kfs110), generating the king cheetah coat variant. [12]

The wild-type (in African wildcats) is the mackerel tabby (stripes look like thin fishbones and may break up into bars or spots). The most common variant is the classic tabby pattern (broad bands, whorls, and spirals of dark color on pale background usually with bulls-eye or oyster pattern on flank). [12] Spotted tabbies have their stripes broken up into spots, which may be arranged vertically or horizontally. A 2010 study suggests that spotted coats are caused by the modification of mackerel stripes, and may cause varying phenotypes such as "broken mackerel" tabbies via multiple loci. If the genes are Sp/Sp or Sp/sp the tabby coat will be spotted or broken. If it is an sp/sp gene, the tabby pattern will remain either mackerel or blotched. This gene has no effect on cats with a ticked coat. [11]

Ticked tabby

The Ticked (Ti) locus on chromosome B1 controls the generation of "ticked coats", agouti coats with virtually no stripes or bars. Ticked tabbies are rare in the random-bred population, but fixed in certain breeds such as the Abyssinian and Singapura. [13] TiA is the dominant allele that produces ticked coats; Ti+ is the recessive one. The causative gene for ticked tabby markings is Dickkopf-related protein 4 ( DKK4 ). [14] Both a cysteine to tyrosine substitution at residue 63 (C63Y) and an alanine to valine substitution at residue 18 (A18V) result in decreased DKK4, which is associated with . Both variants are present in the Abyssinian breed, and the A18V variant is found in the Burmese breed. [13] Stripes often remain to some extent on the face, tail, legs, and sometimes the chest ("bleeding through"). Traditionally, this has been thought to happen in heterozygotes (TiATi+) but be nearly or completely nonexistent in homozygotes (TiATiA). The ticked tabby allele is epistatic to and therefore completely (or mostly) masks all the other tabby alleles, "hiding" the patterns they would otherwise express. [11]

It was once thought that TiA was an allele of the Tabby gene, called Ta, dominant to all other alleles at the locus. [15]

Other genes

Rosette pattern in a Bengal. Paintedcats Red Star standing.jpg
Rosette pattern in a Bengal.

Tortoiseshells and calicos

Female black tortoiseshell and white cat Curlycat02.jpg
Female black tortoiseshell and white cat

Tortoiseshells have patches of orange fur (pheomelanin based) and black or brown (eumelanin based) fur, caused by X-inactivation. Because this requires two X chromosomes, the vast majority of tortoiseshells are female, with approximately 1 in 3,000 being male. [17] Male tortoiseshells can occur as a result of chromosomal abnormalities such as Klinefelter syndrome, by mosaicism, or by a phenomenon known as chimerism, where two early stage embryos are merged into a single kitten.

Tortoiseshells with a relatively small amount of white spotting are known as "tortoiseshell and white", while those with a larger amount are known in the United States as calicos. Calicos are also known as tricolor cats, mi-ke (meaning "triple fur") in Japanese, and lapjeskat (meaning "patches cat") in Dutch. The factor that distinguishes tortoiseshell from calico is the pattern of eumelanin and pheomelanin, which is partly dependent on the amount of white, due to an effect of the white spotting gene on the general distribution of melanin. A cat which has both an orange and non-orange gene, Oo, and little to no white spotting, will present with a mottled blend of black/red and blue/cream, reminiscent of tortoiseshell material, and is called a tortoiseshell cat. An Oo cat with a large amount of white will have bigger, clearly defined patches of black/red and blue/cream, and is called a calico in the US.

Blue tortoiseshell and white (diluted calico) British Shorthair British Shorthair tricolore.jpg
Blue tortoiseshell and white (diluted calico) British Shorthair

With intermediate amounts of white, a cat may exhibit a calico pattern, a tortie pattern, or something in between, depending on other epigenetic factors. Blue tortoiseshell, or diluted calico, cats have a lighter coloration (blue/cream) and are sometimes called calimanco or clouded tiger. [18]

A true tricolor must consist of three colors: white, a red-based color like ginger or cream, and black-based color like black or blue. Tricolor should not be mistaken for the natural gradations in a tabby pattern. The shades which are present in the pale bands of a tabby are not considered to constitute a separate color. [19]

Variations

Tortoiseshell cats with small white patches are called tortillo cats, a portmanteau of Calico and Tortoiseshell. [21]

White spotting and epistatic white

White spotting locus
Bosque de noruega.jpg
Dominant white; solid white Norwegian Forest cat
Co-kbk-07-001.jpg
White spotting; blue (gray) and white bicolor cat

The KIT gene determines whether or not there will be any white in the coat, except when a solid white coat is caused by albinism. White spotting and epistatic white (also known as dominant white) were long thought to be two separate genes (called S and W respectively), [22] but in fact they are both on the KIT gene. The two have been combined into a single white spotting locus (W). White spotting can take many forms, from a small spot of white to the mostly-white pattern of the Turkish Van, while epistatic white produces a fully white cat (solid or self white). The KIT gene W locus has the following alleles: [22] [23] [24]

Colorpoint and albinism

The colorpoint pattern is most commonly associated with Siamese cats, but due to crossbreeding may also appear in any (non-pedigree) domesticated cat. A colorpoint cat has dark colors on the face, ears, feet, and tail, with a lighter version of the same color on the rest of the body, and possibly some white. The exact name of the colorpoint pattern depends on the actual color. A few examples are seal points (dark brown to black), chocolate points (warm, lighter brown), blue points (gray), lilac or frost points (silvery gray-pink), red or flame points (orange), and tortie (tortoiseshell mottling) points. This pattern is the result of a temperature sensitive mutation in one of the enzymes in the metabolic pathway from tyrosine to pigment, such as melanin; thus, little or no pigment is produced except in the extremities or points where the skin is slightly cooler. For this reason, colorpoint cats tend to darken with age as bodily temperature drops; also, the fur over a significant injury may sometimes darken or lighten as a result of temperature change. More specifically, the albino locus contains the gene TYR ( P55033 ). [5] Two distinct alleles causing blue-eyed and pink-eyed albinism respectively have been previously theorized.

Although the Siamese colorpoint pattern is the most famous coloration produced by TYR, there are color mutations at the locus.

The tyrosine pathway also produces neurotransmitters, thus mutations in the early parts of that pathway may affect not only pigment, but also neurological development. This results in a higher frequency of cross-eyes among colorpoint cats, as well as the high frequency of cross-eyes in white tigers. [33]

Silver and golden series

Agouti hair of a brown tabby with phaeomelanin (red pigment) and eumelanin (black or brown pigment). Poil agouti.svg
Agouti hair of a brown tabby with phaeomelanin (red pigment) and eumelanin (black or brown pigment).

Silver series

The silver series is caused by the Melanin inhibitor gene I/i. The dominant form causes melanin production to be suppressed, but it affects phaeomelanin (red pigment) much more than eumelanin (black or brown pigment). On tabbies, this turns the background a sparkling silver color while leaving the stripe color intact, making a cold-toned silver tabby . On solid cats, it turns the base of the hair pale, making them silver smoke. [34] The term cameo is commonly used for red silver and cream silver (inhibitor gene (I-O-)) colored coats in cats.

Wide band factors

Silver agouti cats can have a range of phenotypes, from silver tabby, to silver shaded (under half the hair is pigmented, approx. 1/3 of hair length), to tipped silver also called chinchilla or shell (only the very tip of the hair is pigmented, approx. 1/8 of hair length). This seems to be affected by hypothetical wide band factors, which make the silver band at the base of the hair wider. Breeders often notate wide band as a single gene Wb/wb, but it is most likely a polygenic trait.

Golden series

If a cat has the wide band trait but no silver melanin inhibitor, the band will be golden instead of silver. These cats are known as golden tabbies, or in Siberian cats sunshine tabbies. The golden color is caused by the CORIN gene. Shaded golden and tipped golden are also possible, in the same hair length distribution as the silver-gene. However, there is no golden smoke, because the combination of wide band and nonagouti simply produces a solid cat. [35] [ unreliable source ] [36]

Tipped or shaded cats

The genetics involved in producing the ideal tabby, tipped  [ fr ], shaded, or smoke cat is complex. Not only are there many interacting genes, but genes sometimes do not express themselves fully, or conflict with one another. For example, the silver melanin inhibitor gene in some instances does not block pigment, resulting in a grayer undercoat, or in tarnishing (yellowish or rusty fur). The grayer undercoat is considered less desirable to fanciers.

Likewise, poorly-expressed non-agouti or over-expression of melanin inhibitor will cause a pale, washed out black smoke. Various polygenes (sets of related genes), epigenetic factors, or modifier genes, as yet unidentified, are believed to result in different phenotypes of coloration, some deemed more desirable than others by fanciers.

The genetic influences on tipped or shaded cats are:

Fever coat

Black and white bicolor kitten with fever coat expression over the black fur My adorable little cat (cropped).jpg
Black and white bicolor kitten with fever coat expression over the black fur

Fever coat is an effect known in domestic cats, where a pregnant female cat has a fever or is stressed, causing her unborn kittens' fur to develop a silver-type color (silver-grey, cream, or reddish) rather than what the kitten's genetics would normally cause. After birth, over some weeks the silver fur is replaced naturally by fur colors according to the kitten's genetics. [37] [38] [39]

Fur length and texture

Cat coat hair

Down, awn and guard hairs of a domestic tabby cat Down Awn and guard hairs of cat 2012 11 13 9203r.JPG
Down, awn and guard hairs of a domestic tabby cat

Cat fur can be short, long, curly, or hairless. Most cats are short-haired, like their ancestor. [40] The fur can naturally come in three types of hairs; guard, awn, and down hair. The length, density and proportions of these three hairs varies greatly between breeds, and in some cats only one or two types are found. [40] [41]

Most oriental breeds only express one single layer of silky coat. [40] However, cats can also have double-layered coats out of two hair types in which the down hairs form the soft, insulating undercoat, and the guard hairs form the protective outer coat. [40]

A typical cat coat exists of all three natural hair types, but due to the equal lengths of two of these hairs, the coat is still considered double-layered. [40] Typically, the down hairs comprise the undercoat while the guard and awn hairs make up the basic top coat. [40] [41] Double-coated cats with thick undercoats require daily grooming as these coats are more prone to matting. [40] Double coats are found in for example the Persian, British Shorthair, Maine Coon and Norwegian Forest cat.

Additionally, there even exist cats which express all three natural types of cat hair in different lengths and structures, which form three different layers. These cats are called triple-coated. Siberians and Neva Masquerades are known for their unique triple coats, [40] which provides double insulation to withstand their natural cold climate.

Coat mutations

There have been many genes identified that result in unusual cat fur. These genes were discovered in random-bred cats and selected for. Some of the genes are in danger of going extinct because the cats are not sold beyond the region where the mutation originated or there is simply not enough demand for cats expressing the mutation.

In many breeds, coat gene mutations are unwelcome. An example is the rex allele which appeared in Maine Coons in the early 1990s. Rexes appeared in America, Germany and the UK, where one breeder caused consternation by calling them "Maine Waves". Two UK breeders did test mating which indicated that this was probably a new rex mutation and that it was recessive. The density of the hair was similar to normally coated Maine Coons, but consisted only of down type hairs with a normal down type helical curl, which varied as in normal down hairs. Whiskers were more curved, but not curly. Maine Coons do not have awn hairs, and after moulting, the rexes had a very thin coat.[ citation needed ]

Fur length

Cat fur length is governed by the Length gene in which the dominant form, L, codes for short hair, and the recessive l codes for long hair. In the longhaired cat, the transition from anagen (hair growth) to catagen (cessation of hair growth) is delayed due to this mutation. [42] A rare recessive shorthair gene has been observed in some lines of Persian cat (silvers) where two longhaired parents have produced shorthaired offspring.

The Length gene has been identified as the fibroblast growth factor 5 (FGF5; M3X9S6 ) gene. The dominant allele codes for the short coat is seen in most cats. Long coats are coded for by at least four different recessively inherited mutations, the alleles of which have been identified. [43] The most ubiquitous is found in most or all long haired breeds while the remaining three are found only in Ragdolls, Norwegian Forest Cats, and Maine Coons.

Wavy fur of a Devon Rex cat Wavy fur of a Devon Rex cat.jpg
Wavy fur of a Devon Rex cat

Curly-coated

There are various genes producing curly-coated or "rex" cats. New types of rex arise spontaneously in random-bred cats now and then. Some of the rex genes that breeders have selected for are:

  • Devon Rex
    • Mutation in KRT71 ( E1AB55 ), the same gene causing hairlessness in Sphynx cats. re is an allele completely recessive to the wildtype and completely dominant to hr found in Sphynx. [44]
  • Cornish Rex
  • Ural Rex
  • German Rex
    • Provisionally an allele termed gr. Same locus as Cornish, but proposed as a different allele. However, most breeders consider the German Rex to have r/r genotype.
  • Oregon Rex (extinct)
    • A hypothetical recessive allele termed ro.
  • Selkirk Rex
    • A dominant allele termed Se, although sometimes described as an incomplete dominant because the three possible allele pairings relate to three different phenotypes: heterozygous cats (Se/se) may have a fuller coat that is preferred in the show ring, while homozygous cats (Se/Se) may have a tighter curl and less coat volume. (se/se type cats have a normal coat.) This phenomenon may also colloquially be referred to as additive dominance.
  • LaPerm
    • Provisional completely dominant Lp allele.
Hairless cats are often born even without whiskers Chat Sphynx.jpg
Hairless cats are often born even without whiskers

Hairlessness

There are also genes for hairlessness:

Some rex cats are prone to temporary hairlessness, known as baldness, during moulting.

Here are a few other genes resulting in unusual fur:

  • The Wh gene (dominant, possibly incomplete) results in Wirehair cats. They have bent or crooked hair producing springy, crinkled fur.
  • A hypothetical Yuc gene, or York Chocolate undercoat gene, results in cats with no undercoat. However, the proportional relationship between guard, awn, and down hair production varies greatly between all breeds.
  • A recessive autosomal gene for Onion hair which causes roughness and swelling on the hairs. The swelling is due to enlargement of the inner core of medulla cells.
  • A recessive autosomal gene spf for sparse fur. As well as sparse coat, the hairs are thin, straggly and contorted and there is brown exudate around the eyes and nose and on the chest and stomach. A similar condition is linked to Ornithine Transcarbamylase Deficiency in mice.

Loci for coat colour, type and length

GeneLocus

Name

Locus SymbolsAllele VariantsDescription
ASIPAgoutiAA, APb, aAgouti/tabby, charcoal (cat hybrids, i.e. Bengal and Savannah breeds), recessive black/solid
TYRP1 BrownBB, b, blBlack, brown/chocolate, cinnamon
--OrangeOXO, Xo, YRed, black (sex-linked epistatic)
LVRN / Taqpep Tabby PatternTaTaM, TabMackerel, classic/blotched
DKK4 Ticked TabbyTiTiA,Ti+(Epistatic to tabby) ticked, full body ticked (see Abyssinian)
--Spotted ModifierSpSp, sp(Modifier to tabby) spotted tabby, no modification
TYR ColorpointCC, cb, cs, ca, cFull color, mink, sepia, siamese point, blue eye albino, red eye albino
--InhibitorII, iSilver, non-silver
MLPH DilutionDD, dDiluted color (black=blue, chocolate=lilac, cinnamon=fawn, orange=cream), no effect
--Dilute ModifierDmDm, dmDiluted color modified (blue/brown/cinnamon=caramel, cream=apricot), no effect
KIT WhiteWW, ws, w, wg, wsalSolid white, white spotting, without white, white gloving, white fading
CORIN Wide Bandwb-, wbTabby agouti, shaded, tipped, smoke, silver, golden, "sunshine" (Siberian)
--Barrington BrownBaBa, baDiluted brown (black=mahogany, chocolate=light brown, cinnamon=pale coffee), no effect; Unverified gene
MC1R ExtensionEE, e, er, ecNormal, amber (Norwegian Forest Cat), russet (Burmese), copal (Kurilian Bobtail)
FgF5 Long hairLL, l (M1, M2, M3, M4, M5)Short, long (Ragdoll, Norwegian Forest Cat, Maine Coon and Ragdoll, most longhair breeds, Maine Coon)
KRT71 Curly CoatReSe, se/Re, re, hrCurly coat (Selkirk Rex), normal hair, curly coat (Devon Rex), hairlessness (Sphynx)
LPAR6 Rex (Cornish)RR, rNormal hair, curly coat (Cornish Rex)

See also

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A melanistic mask is a dog coat pattern that gives the appearance of a mask on the dog's face. The hairs on the muzzle, and sometimes entire face or ears, are colored by eumelanin instead of pheomelanin pigment. Eumelanin is typically black, but may instead be brown, dark gray, or light gray-brown. Pheomelanin ranges in color from pale cream to mahogany. The trait is caused by M264V (EM), a completely dominant allele (form) of the melanocortin 1 receptor gene.

<span class="mw-page-title-main">Tortoiseshell cat</span> Two-color coat coloring in cats

Tortoiseshell is a cat coat coloring named for its similarity to tortoiseshell pattern. Like tortoiseshell-and-white or calico cats, tortoiseshell cats are almost exclusively female. Male tortoiseshells are rare and are usually sterile.

Colours of the Syrian hamster can be described in three ways: as "self", "agouti" or "combinations". Self colours are a consistent coat colour with the same colour topcoat and undercoat. Agouti hamsters have a ticked coat, where each individual fur is banded in different colours. Agouti hamsters also have "agouti markings" which consist of dark cheek markings, a dark marking on the head, and a light underbelly. Combinations are produced when two self or agouti colours are present.

<span class="mw-page-title-main">Dog coat genetics</span> Genetics behind dog coat

Dogs have a wide range of coat colors, patterns, textures and lengths. Dog coat color is governed by how genes are passed from dogs to their puppies and how those genes are expressed in each dog. Dogs have about 19,000 genes in their genome but only a handful affect the physical variations in their coats. Most genes come in pairs, one being from the dog's mother and one being from its father. Genes of interest have more than one expression of an allele. Usually only one, or a small number of alleles exist for each gene. In any one gene locus a dog will either be homozygous where the gene is made of two identical alleles or heterozygous where the gene is made of two different alleles.

The agouti gene, the Agouti-signaling protein (ASIP) is responsible for variations in color in many species. Agouti works with extension to regulate the color of melanin which is produced in hairs. The agouti protein causes red to yellow pheomelanin to be produced, while the competing molecule α-MSH signals production of brown to black eumelanin. In wildtype mice, alternating cycles of agouti and α-MSH production cause agouti coloration. Each hair has bands of yellow which grew during agouti production, and black which grew during α-MSH production. Wildtype mice also have light-colored bellies. The hairs there are a creamy color the whole length because the agouti protein was produced the whole time the hairs were growing.

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Further reading