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In rabbits, the wildtype is agouti with a light belly, and a recessive non-agouti allele causes a black coat. A third allele, possibly a mutation to a regulator or promoter region, is thought to cause black and tan color. The nonagouti allele is estimated to have first appeared before 1700. [3]
Agouti-signaling protein is a protein that in humans is encoded by the ASIP gene. [5] [6] It is responsible for the distribution of melanin pigment in mammals.[7] [8] Agouti interacts with the melanocortin 1 receptor to determine whether the melanocyte (pigment cell) produces phaeomelanin (a red to yellow pigment), or eumelanin (a brown to black pigment). [9]
This is not usually seen in dark bays, which have little red in the hair shaft. A mutation to agouti removes the ability to block the black signal, resulting in a fully black horse. [13] The dominant, wildtype, allele of agouti is called A, and the non-agouti mutation is called a. [14]
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; ).
The agouti gene in mice is largely responsible for determining coat colour. The wild-type allele produces a blend of yellow and black pigmentation in each hair of the mouse. This yellow and black blend may be referred to as 'agouti' in colour. [3] One of the mutant alleles of the agouti gene
A cat hair showing agouti coloration A domestic rabbit with agouti coloration. Agouti is a type of fur coloration in which each hair displays two or more bands of pigmentation. [1] [2] The overall appearance of agouti fur is usually gray or dull brown, [3] although dull yellow is also possible.
A recessive mutation in this E gene truncates the protein, producing a non-functional receptor incapable of directing eumelanin deposition in the fur. [16] Among dogs, this mutation is unique to yellow Labrador Retrievers and Golden Retrievers and is thought to have arisen in the retriever population before these individual breeds became distinct.
There is a proposed allele that darkens a bay coat to seal brown, and the sooty gene is linked to other forms of dark bay. Genetically, a chestnut horse is a horse without the ability to produce black pigment, while a black horse does not have dominant agouti to restrict their black pigment to points. The MC1R (extension) either binds alpha-MSH ...