A gene that influences coat color in domestic cats
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Three proteins have been described in humans and mice as being essential for even distribution, transport, and translocation of pigment granules, with defects in these
molecules giving rise to lighter skin/coat color. The dilute phenotype in domestic cats affects both eumelanin and phaeomelanin pigment pathways; for example, black pigmentation combined with dilute appears gray and orange pigments appear cream. The dilute pigmentation segregates as a fully penetrant, autosomal recessive trait. We conducted classical linkage mapping with microsatellites in a large multigeneration pedigree of domestic cats and detected tight linkage for
dilute on cat chromosome C1 (θ = 0.08, LOD = 10.81). Fine-mapping identified a genomic region exhibiting conserved synteny to human chromosome 2, which included one of the three dilute candidate genes, melanophilin (MLPH). Sequence analysis in dilute cats identified a single base pair deletion in exon 2 of MLPH transcripts that introduces a stop codon 11 amino acids downstream, resulting in the truncation of the bulk of the MLPH
protein. The occurrence of this homozygous variant in 97 unrelated dilute cats representing 26 cat breeds and random-bred cats, along with 89 unrelated wild-type cats representing 29 breeds and random-bred cats, supports the finding that dilute is caused by this single mutation in MLPH (p < 0.00001). Single-nucleotide polymorphism analyses in dilute individuals identified a single haplotype in dilute cats, suggesting that a
single mutation event in MLPH gave rise to dilute in domestic cats. dilute Linkage mapping Microsatellite Melanophilin (MLPH) Domestic cat Coat color Pigmentation Eumelanin Phaeomelanin Cited by (0)Copyright © 2006 Elsevier Inc. All rights reserved. Cats from all over the world display a great variety in expressions of cat coat colour and for this reason were always a subject of research in fields of genetics and inheritance. Influence of certain genes on the cat’s coat colour can be relatively easy to explain, while some of them may be more complicated than expected. The reason for this is because genes do not act in isolation, independently from other
genes. In the following article, we will mention some of the main loci recognized that affect the coat colour, and explain they influence on the phenotype, as well as their influence on the expression of other cat coat colour genes. The cat coat colour, eye, and skin colour is a result of present pigments. Two main pigments responsible for the coat colour and eumelanin, which is seen as a black or intense brown pigmentation, and phaeomelanin, recognised a red-yellow pigmentation. Agouti cat with tabby pattern BLACKB locus stands for ”black” since the dominant gene of the locus is expressed in the black coat colour. Genes of the B locus influence the expression of only eumelanin. Two mutations of the B gene have been identified, b (brown or chocolate) and bl (light brown or cinnamon). The chocolate (b) allele is dominant over the cinnamon (bl) allele. Since the B gene is dominant over the locus, cats heterozygous for it ( Bb or B bl genotype), carry chocolate or cinnamon gene but it cannot be recognized based on phenotype. DILUTIONA mutation at the D locus results in coat colour dilution when both present alleles are mutated. Such genotype can be recognized as Blue, Lilac and Fawn phenotype. The reason for this colour dilution is the clustering of the pigment particles in the hair shaft. Blue is the dilute form of Black; it is commonly seen as various shades of gray. Lilac is the dilute form of Chocolate; it is described as dove or light grey and is sometimes called lavender. Fawn is the dilute form of Cinnamon; it is described as a caramel colour. Influence of the D locus genes on the black coat color: black and blue cat ORANGEOrange, or the O gene, is located on the X chromosome, and is, therefore, sex-linked trait. There are two types of alleles of the O gene, the orange (O) allele, and the non-orange (o) allele. The O gene is dominant, and when present, it leads to phaeomelanin production and inhibition of the black pigment. As an X-linked gene, males can be O or o, while females can be OO, Oo, and oo. Male O and female OO cats are red in colour, while Oo females are known as calico, with red and black pigmentation present in the coat colour. The orange gene on O locus has not yet been identified. When possessing orange and black coat color genes, a male cat will express only the orange coat color. A female cat with both coat color genes will be recognized as a tricolor or calico cat. COLOURPOINTThe colourpoint pattern is commonly associated with Siamese cats but can appear in the domestic cats as well. The C locus genes belong to the so-called Albino series and are in following hierarchical order: C (full colour) > cb (Burmese) = cs(Siamese) > c (complete albino). The C gene, also known as the Himalayan gene, codes for the tyrosinase enzyme, which is necessary for the production of melanin. Mutations in the C gene result in phenotypes with different degrees of pigmentation, as a result of a temperature sensitive mutation in the metabolic pathway from tyrosine to pigment. This is results in better pigment production at the extremities, which are cooler, such as the face, tip of the tail and paws, and therefore look darker than the warmer body parts. Burmese cats are recognized by their dark sepia brown coat colour which is a result of the cb gene. Although this colour is typical for the Burmese cat breed, not all Burmese possess this gene. Siamese express the temperature dependent pigmentation the most evidently, with darker parts of the coat in the ears, muzzle, feet and tail tip. Siamese cats exhibit coat color typical for the temperature sensitive mutation within the C locus, which results in better pigment production at the colder extremities, which are cooler, such as the face, tip of the tail and paws. Albino cats are recognized by the white coat and blue eyes. The albino mutation causes a premature stop codon in the tyrosinase gene. The mutation is recessive and the albino cats are homozygous for the mutation. Since the tyrosinase gene is essential in multiple biochemical pathways, albino cats are usually deaf. Cats heterozygous for the albino gene are not completely albino and have one eye pigmented, a phenotype also known as the ‘’odd-eyed’’. Such cats are usually deaf only on one ear, the one closer to the albino blue eye.
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