RAINBOW OF GINGER THE COLOUR GENETICS

The colour genetics of the Rhodesian Ridgeback are quite simple compared to the color genetics of most other dog breeds. But at the same time, we can say with all confidence that the Ridgeback has the widest palette of red shades, which makes it unique and undoubtedly extremely beautiful!

Let’s remember what the standard tells us about color.

Colour: from light wheaten to red wheaten. Head, body, legs and tail of the same tone. A little white on the chest and toes is permissible, but excessive white hairs here, on the stomach, or above the toes is undesirable. A dark muzzle and ears are permissible, it is desirable that it be bright and intensely coloured. The presence or absence of a mask cannot be a criterion for the quality of a dog.

Excessive black hairs throughout the coat are highly undesirable.

The nose is black or brown. Dark eyes correspond to a black nose, amber to brown. Among breeders, a stable definition of brownnosed Ridgebacks is accepted – they are called “liver”.

From the Rhodesian Ridgeback breed standard:

Colour: Light wheaten to red wheaten. A little white on the chest and toes is permissible, but excessive white hairs here, on belly, or above toes is undesirable. A dark muzzle and ears permissible. Excessive black hairs throughout the coat are highly undesirable.

EYES: Should be moderately well apart, round, bright and sparkling, with intelligent expression, their colour harmonising with the colour of the coat.

Nose: The nose should be black or brown. A black nose should be accompanied by dark eyes, a brown nose by amber eyes.

Colour Genetics

The colour of the coat of an animal depends on the type of pigment, the shape of the pigment granules and their distribution throughout the hair. The whole variety of colours in mammals is due to the presence of melanin pigments, represented by two forms: eumelanin and pheomelanin, synthesized in the form of pigment grains (granules) of various shapes.

The perception of colour depends on the refraction of light passing through them or reflected from them. Eumelanin granules have a somewhat elongated ellipsoidal or spherical shape and can vary quite a lot in size. Eumelanin has two modifications: black and brown. Pheomelanin granules are characterized by a classic yellow or orange colour. They are spherical and much smaller than eumelanin granules.

In most coloured animals, both pheomelanin and eumelanin are formed in the same hair follicle, respectively, and both types of pigments are simultaneously present in the hair. But it is important to note that only one type of eumelanin and only one type of pheomelanin can be present at the same time.

MAIN ALLELES OF THE RHODESIAN RIDGEBACK Ginger

The red colour of the Ridgeback can have different shades: from light tones – light wheaten, straw­red – to golden­red and red­ginger and even almost brown. The main colour forming alleles of this color are Ау/Ау E(Em)/E(Em) ky/ky.

At the same time, in the colour, the eumelanin zone (darker ­ brown / black) is shifted to the end, and the pheomelanin zone (yellow / red) – to the base of the hair. This colour has the common name sable, in the Rhodesian Ridgeback breed –wheaten.

Locus A (ASIP)

Under the influence of the Ay allele in the hair follicle, at a certain moment in the growing hair, the synthesis of eumelanin switches to the synthesis of pheomelanin, that is, there is agouti, a yellow pigment appears. As a result, the eumelanin zone is at the end of the hair, and the pheomelanin zone is at the base of it. And whether the ridgeback will be wheaten or dark red depends on the ratio of these melanins in the hair. Since eumelanin synthesis is more active in the initial stages of hair growth, puppies of this colour are born almost black and brighten with age. The relative intensity of pigment synthesis may depend on many factors, including: the expressivity of the Ay gene itself, modifier genes, the hormonal background of the dog, metabolic characteristics, etc.

The colour of the Rhodesian Ridgeback is essentially zoned red, where a reddish stripe of a more saturated shade forms on the back. On the neck, shoulder blades, back of the thighs, belly and underside of the tail the colour is a lighter shade than the main tone. This colour is without any admixture of black hair, excluding the muzzle and ears in the presence of a mask. According to the standard for the Rhodesian Ridgeback, excessive blackening of the red color is a serious fault. Previously, such blackening (darkening) of the color could not be determined by testing, but thanks to recent research, it has become possible.

In the very last days of a severe pandemic year of 2020, geneticists from the Universities of Bern and Stanford shared what is probably the most significant discovery in the field of dog colours in the past few years. The authors studied the work of the agouti gene (locus A) in dogs and identified the basic principles of regulation. This allowed the discovery of a new series of mutations, some of which more accurately predict the diversity of agouti colours than previously described variants, and even explain the genetic differences between two very similar manifestations of the dominant red ­ red Ay and black­red Ay. Numerous studies have been carried out, on the basis of which it is now possible to speak about the presence of more alleles of the A locus than previously thought.

Ay > Ays > aws > aw > asa ( asa1, asa2, asa3) = at ( at1, at2, at3)> a.

Ay > (clear sable) agouti/dominant red ­ a clear red with lighter and more saturated areas (present in the breed, confirmed by tests).

Ays > (shaded sable) darkened agouti/sableblack ends of hairs all over the body, with an increase in the intensity of black accumulation in the neck, forehead, back, tail. (present in the breed, confirmed by tests) aws >(saddle agouti) black­haired agoutiblack ends of hairs mainly in the dorsal region, forming a saddle pattern on the dog’s back. (probable in breed, not tested) aw > (agouti) zonal / “wolf” ­ intense blackening along the body like “sable”, with a minimum amount of red or its complete absence. (improbable in the breed) asa (asa1, asa2, asa3) > (saddle) black hairs on the back of the dog forming an intensely colored saddle pattern (improbable in the breed) at (at1, at2, at3)> black and tan (tanpoint/ black&tan) ­ black colour with red areas in permanent areas: eyebrows, cheeks, throat, shoulders, underside and inside of the paws. (present in the breed, confirmed by tests) asa/at – dogs with this type of genotype have an intermediate colour like asa/asa dog, but with a characteristic dark “cap” on the head a ­ (recessive black) black ­ solid black colour (improbable in the breed).

Until recent studies, it was only possible to determine by testing Ay ­ dominant red, aw ­ zonal, at ­ black and tan and a ­ black (recessive). And the different degree of darkening of the red was explained by a combination of alleles of the A locus.

All alleles of the A locus are different haplotypes ­ a combination of mutations in the agouti promoters that control the operation of the gene. VP (Ventral Promoter) ­ 2 options, and HCP (Hair Cycle Promoter) ­ 5 options. And their different combination determines the diversity of alleles of the agouti locus.

This table shows combinations of different mutations. 2 types of VP (Ventral Promoter) and 5 types of HCP (Hair Cycle Promoter). And the Ay, Ays and at alleles are present in the breed, and this is confirmed by tests as well.

The alleles aw, aws, asa, and a are probable but doubtful and not tested. I once saw a dog with the aws or asa phenotype, when there were no such tests available. The dog was definitely purebred. And we see similar to these ones even now. Here is an example, but these may all just be variations on the sable agouti.

Dogs with the allele a ­ recessive black are likely but uncertain. A lot of dogs have been tested, the test has been done for a long time and the a-allele has not been identified anywhere – several researchers have collected statistics. While we were looking for illustrations, we found several black mixed breed dogs, which are not recessive black, but dominant, where one black ancestor is enough. One dog was introduced to us as a ridgeback, but objectively this is extremely doubtful. But since we have no official evidence of impure breeding, the presence of this allele in the breed is not completely excluded.

Locus А (ASIP)

Ay > Ays > aws > aw > asa ( asa1, asa2, asa3) = at ( at1, at2, at3)> a.

Ays > (shaded sable) darkened aws >(saddle agouti) black-haired agouti aw > (agouti) zonal / “wolf”/ “wild” asa > (saddle) at > black and tan (tanpoint/black&tan) a-recessive – black - solid black colour (improbable in the breed)

2 types of VP (Ventral Promoter) and 5 types of HCP (Hair Cycle Promoter).

The alleles aw, aws, asa, and a-recessive are probable but doubtful and not tested

And the Ay, Ays and at alleles are present in the breed, and this is confirmed by tests as well.

I once saw a dog with the aws or asa phenotype, when there were no such tests available. The dog was definitely purebred.

And we see similar to these ones even now. Here is an example, but these may all just be variations on the sable agouti.

Dogs with the allele a - recessive black are likely but uncertain.

On photos below you see dogs with blackening, sables with varying degrees of blackening. A liver dog will also be sable, but the tips of the coat of a liver dog will be brown, so the sableness of a liver dog will not stand out as sharply as a black­nosed dog. But a sable liver will also pass this allele on to all its children, who, with a black nose, will look like typical sable.

Locus E - (extension) ­ determines the distribution of black or brown eumelanin throughout the body of the dog, without changing the amount of yellow pigment.

Major alleles of the locus

The order of dominance at this locus is:

Em > Eg > E > Eh > e­recessive

Alleles present in the breed:

Allele Em ­ dark mask

The mask refers to the spread of black or brown pigment on the muzzle, and often on the front of the head, up to the ears. The color­forming allele of the mask is the dominant allele Em, which can show different degrees of expressiveness.

All these dogs are Ays/Ays: blacknosed and livers

Locus E - (extension)

Major alleles of the locus

The order of dominance at this locus is:

Em > Eg > E > Eh > e recessive

Alleles present in the breed: Allele E-dominant is a simple uniform distribution of eumelanin without zones of intensity.

Allele E-dominant is a simple uniform distribution of eumelanin without zones of intensity.

Alleles absent in the breed:

Allele Eg (extension grizzle) ­ grey and tan, which is inherent in greyhounds and some other breeds.

The Eh allele has been found in English Cocker Spaniels.

Ginger colour due to alleles e/e

The recessive gene e in the homozygous state prevents the distribution of eumelanin throughout the body of the dog. Dog ­ carriers of these alleles, regardless of the color formula, have a uniform red colour. Eumelanin is concentrated only in the skin and the iris of the eyes. Puppies of this colour, unlike puppies of sable colour, are born pure red, without the slightest hint of blackening. Alleles e/e are epistatic ­ dominant in relation to all other color genes, therefore, red, especially lightened, dogs can be hidden carriers of any gene (dominant black, brindle, marble, etc.). Therefore, crossing such individuals with dogs of other colours often leads to unexpected results. For example, beautiful bright red Irish setters are genetically ... black or black&tan, but under the influence of alleles e/e ­ red.

The presence of a red colour of this type in Rhodesian Ridgebacks has not been confirmed by genetic tests, but it is not excluded either, since an insufficient number of studies have been carried out to completely exclude these alleles in the breed.

Intensity and shades of red colours

Red dogs have very different intensities and shades, which depends on the many brightening factors acting on pheomelanin, its location in the hair, the thickness and transparency of the cortical layer, etc. It also depends on the presence of alleles of a polygenic action, that is, the action of several genes that affect concentration of pheomelanin in the hairs. Shades of red colors may depend on the types of pheomelanin, as well as on other alleles that have a lightening effect on the color (d-dilute, G ­ age lightening, like in Kerry Blue Terriers, etc.). The combination of action of all these genes can lead to a very strong, up to almost white, lightening of the red color of dogs. There is also an assumption about the possible polygenic inheritance of the red color according to the type of cumulative polymerization ­ the cumulative interaction of several pairs of genes with a similar effect. A similar assumption was put forward by the famous American genetics researcher Clarence Cook Little, speaking about the presence of rufus polygenes that affect the intensity of the colors of the pheomelanin group.

In recent years, several genetic factors associated with the features of pheomelanin synthesis have been discovered. Thus, it is assumed that the lightening of pheomelanin, leading to the appearance of cream, fawn colors, is associated with mutations in the MATP genes ­ locus I (MFSD12), KITLG, CHR2, CHR18, CHR21. These mutations are responsible for 70% of the color lightening variations.

Empirically, we excluded the influence of locus I in our breed by testing dogs of different color intensities and getting the same result I/I for all.

The work of mutations in the KITLG gene determines the saturation of the colour ­ the more copies of mutations in this gene, the richer the colour. For example, the Irish Setter is the owner of the largest number of copies in this gene, and this gene is also responsible for the variability in colour saturation in poodles.

Alleles absent in the breed: Allele Eg (extension grizzle) - grey and tan, which is inherent in greyhounds and some other breeds. The Eh allele has been found in English Cocker Spaniels.

The three recently discovered loci CHR2, CHR18, and CHR21 are not yet well understood. Their various combinations lead to different color intensity, the mechanism of which is not yet clear. The laboratory that tests for these mutations, unfortunately, without a detailed explanation, gives the result “dark, medium, light” with a brief description of the fact that there are genes that are responsible for 70% of redhead intensity cases.

Locus D - dilution.

The exact genetic designation is dilutes or pales eumelanin pigment to blue, and phaeomelanin subtly (MLPH). This locus determines the innate intensity of pigmentation.

Major alleles of the locus (currently being tested)

Allele D-dominant

• Allele d-recessive (d1, d2, d3)

Allele D ­ determines the normal form of melanocytes and ensures the development of pigmentation of full intensity.

Allele d ­ causes the development of congenital weakening of the colour. Under the action of this allele, pigment granules stick together. In this case, the number of granules does not decrease, but they stick together into random groups, as a result of which their uniform supply to the growing hair is disturbed, which leads to the appearance of separate voids in the hair shaft and uneven accumulation of granules in different parts of the hair. This in turn leads to a strong decrease in the absorption of light by the hair tissues and a phenotypic weakening of the colour. In the homozygous state, this allele causes the birth of clarified puppies.

An association with a recessive allele associated with alopecia is suspected.

Possible mutations in the KITLG gene, locus CHR2, CHR18, CHR21 and any another factors

Locus K (dominant black, solid black)

Major alleles of the locus

• Allele К (КВ) ­ dominant solid black (absent in the breed)

Allele кbr – brindle (absent in the breed)

• Allele k (ky) – present in the breed

Allele K (KB) ­ determines the continuous distribution of eumelanin in the hair and body of the dog. It is this allele that has received the name “dominant black” in our time. Under its influence, black or brown eumelanin is evenly distributed over the hair and body of the dog, forming a continuous uniform colour.

Allele kbr ­ (Brindle) ­ brindleness ­ causes an uneven distribution of pigments over the body with the formation of vertical stripes of varying intensity.

The brindle colour can vary greatly in the width of the stripes and the colour of the main background, which is due to the interaction with the alleles of other loci and the influence of modifier genes.

Brindle dogs are 99% absent in the breed. We leave 1% for the off chance of some line, where, in addition to the brindle, there is a recessive red, which hides everything under itself and stably meets a partner with an allele of a recessive red colour, which is also extremely doubtful, since the test has existed for a long time and has never been statistically revealed.

The probable detection of alleles a, kbr and e will rather indicate the crossbreeding and fusion of dogs of other breeds.

The ky-allele is a recessive allele of the locus that does not prevent the manifestation of the A­locus alleles. Present in wild, sable, black­backed and tan dogs. Hypostatic in relation to a pair of alleles a/a.

At this locus, the K-allele completely dominates over the kbr and ky-alleles.

K > kbr > ky

Locus B (Black/Brown).

Major alleles of the locus

• Allele B

Allele b (bc, bd, bs)

Allele B ­ provides the formation of black eumelanin. This allele has in the gene pool dogs of all colors except brown and fawn with a pink nose. Allele b ­ contributes to the formation of a brown pigment. For its formation, the presence of a pair of recessive bb genes is necessary.

Until relatively recently, only these two alleles have been described in dogs. At the same time, in animals of many species, for example, mice, guinea pigs, cats, this locus is described as a series of multiple alleles. Biochemical studies of recent years confirm the presence of several brown alleles in dogs ­ bc, bs, bd. These alleles provide different shades of brown. It is almost impossible to talk about the order of their dominance over each other. It is also impossible to talk about any kind of breed affiliation of these alleles, there are no extensive studies on this topic, and phenotypically, their carriers also differ little from each other.

Allele B completely dominates over all alleles b, that is, the synthesis of black pheomelanin completely suppresses the synthesis of brown, i.e. black colour completely dominates brown.

In breeds where the KB and kbr-alleles are present, the B­locus is responsible for the color of the nose, eyelids, claws, and coat of the dog. In our breeds with ky/ky-alleles, locus­B is responsible for the colour of the nose and eyelids, as well as the colour of the darkening in the case of a “sable” dog.

White spotting

White spotting is quite common in Ridgebacks and has a very wide variability. A genetically spotted dog may be solid with a few white hairs on the chest or be almost white with a small dark spot at the end of the ear. Several recessive genes from a series of multiple alleles related to the S locus cause white spotting. These genes cause depigmentation, or, in other words, a break in pigmentation in different parts of the dog’s body.

The extent of depigmentation zones may depend on a number of alleles.

A series of multiple alleles of the S locus includes the following genes that cause spotting of varying degrees: sW-allele is an extreme degree of spotting, when small dark areas remain in the pigment centers.

Allele S ­ solid colour.

Allele si ­ small white areas in the primary centers of depigmentation, the so­called “Irish spotting”. sp-allele is piebald, in which up to 30% of the body is white, such a dog is no longer called piebald, but spotted.

There is incomplete dominance between si, sp, sW, but S completely dominates all of these alleles. In Rhodesian Ridgebacks, only Irish spotting is allowed, which is mildly expressed.

Molecular genetic analysis confirms the presence of different alleles at this locus, but there is no way to visually identify them. In addition to different alleles of the S locus, the development of white spotting is influenced by numerous modifier genes.

Here are dogs with varying degrees of whiteness. Unfortunately, while tests cannot reveal different alleles of inheritance of white spotting, breeders are left to use the old-fashioned method - selection of pairs.

Colour anomalies not related to colour loci:

Snow nose and Dudley nose ­ the nose of a dog is black or brown in colour, having lightening, sometimes full, to pink of varying degrees of intensity and different areas. Snow nose is seasonal and is associated with a seasonal lack of an enzyme that affects the synthesis of melanin.

Dudley nose has a permanent character, when external conditions change, pigmentation is not restored. That is, in order to understand the difference between a snow and Dudley nose, we look out the window and at the thermometer. Cold? Snow nose. Warm? Dudley nose.

And also, the Ridgeback can have problems such as vitiligo, mosaicism and chimerism. But this is a completely different story, which has nothing to do with the genetics of colours.

Vitiligo* is a violation of the production of melanin, and as a result, discoloration in the skin, coat, claws, and iris of the eyes.

A chimera* is an organism resulting from the fusion of two or more zygotes. That is, black spots on a red dog may be cells of littermates that have merged into one organism at an early stage of development.

Mosaic* is a mutation in the cells and tissues of one organism. For example, most merle dogs are mosaics. Or, like a Ridgeback, a spontaneous mutation.

Chimerism or mosaicism is in front of us, it can only be established for sure by testing different cells.

The basic colour formulas for a Ridgeback that does not carry a non­standard colour:

• Ay/Ay E/E B/B D/D ky/ky si/si ­ black­nosed dog without a mask

Ay/Ay E/E b/b D/D ky/ky si/si – liver dog without mask

Ay/Ay Em/Em(E) B/B D/D ky/ky si/si – masked black­nosed dog

Ay/Ay Em/Em(E) b/b D/D ky/ky si/si – liver dog with mask

But how wide and beautiful the palette of red wheaten in the Ridgeback is, as the Ridgeback itself is just as beautiful and multifaceted!

WRITTEN BY BARBARA TURPIN , OF COURSE RHODESIAN RIDGEBACKS, CANADA