11.4 Colour genes in domestic animals

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The inheritance of coat colour in the Danish swine breeds are regulated by the following three loci, see also Figure 11.5.

Dominant                   Recessive                 
White           I-          Coloured    ii              
Black           E-          Red         ee              
Uniformly       ii          White belt  i(be)i(be)

The Landrace (L) and the Yorkshire (Y) breeds are homozygotic for dominant white, II.
The Duroc (D) race is red, eeII.
The Hampshire (H) race is black with a white belt, EEi(be)i(be).
Figure 11.5
The Landrace and Yorkshire are homozygote for dominant white, the Duroc is red and the Hampshire is black with a white belt

Most of the pigs produced in Denmark have an LY mother and a coloured (D or HD) father. They are all white as they are heterozygote with respect to the genotype Ii. Marklund et al. 1998, Genome Res. 8:826-33, has shown that the dominant white in swine is caused by an allele in the kit gene, which corresponds to the mast cell's growth factor receptor. The extension locus code for the colour difference between the black and red pigs.

Details of the belt gene is given in Mamm Genome 1999 Dec;10:1132-6 af Giuffra E et al. it is an allele in the kit gene.

The inheritance of coat colour in the Danish cattle breeds are regulated by the following three loci: `

Dominant                   Recessive                 
Black          E-          Red       ee              
Uniformly      S-          Spotted   ss
White head     SH-          Uniformly SS

The Danish Holstein Frisian dairy breed (SDM) has the genotype EEss and The Danish Red dairy breed (RDM) has the genotype eeSS. Crosses between SDM and RDM become uniformly black. Some RDM have a different colour pattern, tiger stripes, which are cased by an allele in the e locus which dominates over red colour.
In some Danish beef cattle breeds, for instance Hereford, white head colour pattern occur, having dominant inheritance. It is inherited from a dominant allele in the same locus as spotted. It is known, that the gene for spotted is situated on chromosome 6, and is tightly linked with the kit gene and it has interaction with the kit gene.
Figure 11.6.
Danish Holstein Frisian with the genotype EEss and Danish Red with the genotype eeSS. The Hereford has the dominantly inherited white head.

Klungland et al. 1995, Mammalian Genome 6:636-39, have shown that red colour in cattle is caused by the ee genotype in the extension locus.

Inheritance of coat colour in dogs, by Helle Friis Proschowsky
The inheritance of coat colour in dogs is very complex, therefore only the main types will be described here.
In some breeds the coat colour is very constant, thus all individuals have the same coat colour. But each breed has its own special set of colour genes and some breeds have great variation. People with special interested in a particular breed can consult 'The inheritance of coat colours in dogs' by Clarence C. Little, Howell Book House, 1984.

A short description of the best known colour loci and their significance for the coat colour in dogs:

Locus A: Determines the amount and the localization of dark and light pigment, both for the individual strands of hair and for the fur as a whole. The allele at , for instance, causes the black and tan colour of Rottweilers, Airedales and Gordon setters.
Locus B: Determines the amount of dark pigment and whether the colour should be dark (B-) or liver brown (bb).
Locus C: Determines the depth of the pigmentation. The allele ca , gives albinos, and the chinchilla allele cch which makes the reddish and yellow colours become cream colour in for instance Cocker Spaniel. The chinchilla allele also gives rise to large variations in the depth of the pigmentation, in for instance Chesapeake bay retriever and Tibetan Terrier.
Locus D: Determines the intensity of the colour. The allele D gives an intense colour (black in Grand Danois), while the allele d gives a bluish dilution. Weimarans always carry the Recessive dd along with bb, thereby yielding the liver brown coat colour.
Locus E: Determines the pattern of the pigmentation in the coat. Alleles Em, for instance gives the Leonberger a black mask and the allele eb gives the Boxer and the Grand Danoi tiger strips (brindle), while the genotype ee produces the Labrador Retriever's yellow colour.

Figure 11.7 The black and tan colour in the Airedale, atat. Dilution colour in the Tibetan, dd, and yellow colour from the extension locus in the Labrador retriever, ee.

Locus G: alleles in this locus determine whether or not the colour fades with age.
Locus M: the dominant allele M gives merle colour (Collie, Shetland Sheepdog), while the Recessive allele m gives a uniform pigmentation. It is well known that two dogs carrying the merle colour should not be mated, as a double dose of the allele often causes damage to the eyes and the sense of hearing.
Locus S: determines whether or not the coat have spots. The dominant allele S gives a uniform pigmentation, though occasionally with white spots on the feet and/or the chest (Retriever, Boxer and New Foundlander). The three more Recessive s-alleles give varying amounts of white spots, the Clumber Spaniel and the Dalmatian being mostly white.

Inheritance of coat colour in the cat, by Nan Hampton, University of Texas at Austin, who also has an elaborated power point show with about 50 slides.

Below is shown a table of some of the more common genotypes and phenotypes of the domestic cat.

Common Genotypes and Phenotypes
Homozygous Homozygous Heterozygous
Genotype Phenotype Genotype Phenotype Genotype Phenotype
AA agouti aa non-agouti (black) Aa agouti
BB black pigment bb brown pigment Bb black pigment
CC full color cbcbcscs burmesesiamese CcbCcscbcs full colorfull colortonkanese
DD dense pigment dd diluted pigment Dd dense pigment
ii full pigment II pigment limited to tips of hairstrand, base of hair light gray or white, agouti especially affected by agouti=silver tabby with non-agouti=smoke with orange=cameo
LL short hair ll long hair Ll short hair
mm long tail MM lethal on prenetal stage Mm short tail
oo or oY non-orange (usually black) OO or OY orange Oo tortoiseshell=orange and black in females
ss no white spots SS white spots > 1/2 body Ss white spots < 1/2 body
TT mackerel stripe TaTatbtb Abyssinianblotched TTaTtbTatb Abyssinian, faint leg and tail stripes Mackerel stripes Abyssinian, faint leg and tail stripes
ww not all white WW all white Ww all white

Inheritance of coat colour in mink
Mink's colour types have evolved through selection or mutations of colour genes. The wild genotype for colour, which has no mutations, is called Standard and ranges from dark brown (wild mink found in nature and the colour type Wild mink) to the strongly selected farm mink Black standard, which is totally black. This is due to selection for darker colour in the last 40 generations.

The mutated colour types in mink are classified according to numbers and types of genes responsible for the appearance of the colour. Until now it has not been possible to correlate the mink colour genes with the colour genes described in other mammals. The only exception is the albino locus. Hopefully this problem will be solved in the near future by means of DNA technology.

The Recessive and dominant colour genes: Single Recessive colours stem from homozygosity in mutated Recessive genes. Colour genes from two or more mutated colours, having originated from the same wild (standard) genes, are called allelic genes and will occupy the same chromosomal location (locus). The homozygous state of dominating genes is often lethal, resulting in a reduced litter size when heterozygotes are mated. Only the most commonly used combinations of the mutations are shown. A cross between non-allelic mutations results in the dark brown colour. This was the common type when the mutations originally were established.
Colour types, single Mutation name Mutation genotype Wild type, Standard
White Albino, red eyeds cc CC
Hedlund White, deaf hh HH
Grey Aleutian, bluish aa AA
Silver Blue, grey pp PP
Steel Blue psps PP
Brown Royal Pastel bb BB
Moyl mm MM
American Palomino kk KK
Bicoloured Black Cross Ss ss
95 % White SS ss
Finn Jaguar Zz zz
Bicoloured Pastel Cross bb Ss BBss
Bluish grey Sapphire aa pp AAPP
Blue Iris aa psps AAPP
Sand Pearl mmpp MMPP
Light sand Violet aakkpp AAKKPP

Combination types used as production crosses. The crossing of non-allelic Recessive genotypes is practiced to produce various dark brown shades (called Demi buff, Glow or Wild mink).

The following three crosses (F1) are commonly used to produce the Glow type

    Sapphire x Pastel 
    Pearl    x   "
    Violet   x   "
            F1     x   Wild mink

The Pastel is the female due to its high fertility. The F1 female can be crossed with Wild mink. The F1 female is very fertile and the offspring will maintain the Glow colour type as the Wild mink breed true for the Standard genes. The Mahogany colour type is produced by crossing Standard black and Wild mink. This gives a very dark brown mahogany colour type. The Mahogany F1 can be used in further breeding with the same result, therefore a pure bred Mahogany line can be established.

References: Experience from farm practise.
Nes, N., et al. 1988. Beautiful Fur Animals and their Colour Genetics. Scientifur, 60 Langagervej, DK-2600 Glostrup.

Below is shown mink colour types from the book Beautiful Fur Animals, with permission from Outi Lohi.

Colour genes in the horse
For a detailed description of the horse colour genes reference can be made to 'The horse coat colour genetics' from the Model Horse Reference website.
Horse Colours Genetics or from the Veterinary faculty in Davis, California Horse Colours

The most important horse colour genes with indication of back ground colour genes :

Agouti locus (A locus)back ground CCEE
Dominant bay, A- Recessive black aa
Cremello locus (Cr locus) back ground aaee
'Codominant' chestnut, CC Heterozygot, CCr 'Recessive' light, CrCr
Extension locus (E locus) back ground aaCC
Dominant black, E- Recessive chestnut, ee
Grey locus (G locus) back ground AACCEE
Dominant grey, G- Recessive bay, gg
Roan locus (R locus) back ground AACCEE
Heterozygot roan Rr Recessive bay, rr Dominant RR, die
Dominant white (W locus) back ground AACCEE
Heterozygot white Ww Recessiv bay, ww Dominant WW, die

The colour genes work in concert, the types shown above are representative for a group, in the real world there is a continuum of colours due to modifying genes.
The genes in the agouti and extension locus works as earlier mentioned together, so if a horse should be black it shall have the genotype aaE-; an aaee horse has chestnut colour. There is also interaction between all other colour genes.
Roan and ekstension locus are linked.
Locke et al. (2001) Animal Genetics 32:340-343, have shown that the cream dilution, Cr, allele is not coded from the C locus, as earlier symbols have indicated. The gene is not homologous with the tyrosinase gene in other species.

Other species
The rabbit's coat colour genetics reference is to Jackie Carey's Rabbit Colour Genetics

Chapter 11