Cocker Coat Colour Genetics
- Cocker Spaniel Coat Colours – Photos
- Cocker Spaniel Solid Colour Examples
- Cocker Spaniels Parti-Colour Examples
- Cocker Spaniel Blue Roan Development Examples
- Cocker Spaniel Orange Roan Development Examples
- Cocker Spaniel Parti Colour Development Examples
Courtesy of Chris @ http://www.powerscourt-cockers.co.uk
Coat colour inheritance in the Cocker Spaniel is an interesting subject,and a complete minefield. The cocker has a huge variety of coat colour/pattern combinations and this not only serves to make things interesting for us in terms but also often makes the whole process seem mind boggling at times!
Despite the obvious complexities of explaining colour inheritance, when you look closer it is not hard to understand if you take things one step at a time. The coat colour example pages should help to clarify the pattern of inheritance as the explanations alone can look quite daunting.
Coat colour probability is a very imprecise science due to a number of factors:
- Theoretically, Mendelian Law determines that we should be able to predict the coat colour of a puppy (given that the parents carry for identical colours – dominant or recessive) in a set ratio of 3 : 1. However, this is not always the case. For example we have the red parents (mentioned later), who are not genetically recessive (‘ee’) who are able to produce a dominant colour i.e. Black.
- With Mendelian inheritance, there is the “Law of Independent Assortment.” In independent assortment, the chromosomes that are given to a newly-formed gamete (potential puppy) by each parent (one for each ‘trait’ from each parent) are randomly sorted from all possible combinations of maternal & paternal chromosomes.
- Because of the “Law of Independent Assortment” and because ratios are calculated in percentages, unless the same two parents produce 100 offspring together (probably impossible!!) the difference between expected outcomes and actual results can vary hugely due to the small sample size i.e. a litter containing 6 pups as opposed to 100 puppies! Therefore, in the interim the balance of coat colours is likely to be significantly different.
- Finally, there is the law of chance, an unknown & unpredictable phenomenon that causes an event to result one way rather than another which means, that despite all other factors being equal, it is still probable that a predicted coat colour is elusive! Therefore, all the probabilities shown on the example pages represent expectations averaged over the long run & are subject to Mendel’s ‘Laws’.
Coat (fur) colour is created by the pigments contained within the hair (pigmentation also occurs in the skin and eyes). The two main pigments are “phaeomelanin” (yellow) & “eumelanin” (which has two subtypes of black or brown). These are responsible for the colour and the amount, extent and distribution of these pigments, both individually in combination, or in competition with one another and are controlled by the loci (a chromosome [allele] that is occupied by a specific gene).
Pigment in the coat is formed by the interaction of two types of substances. One is widespread and basic to the survival of the animal; this is called a chromogen (a chemical compound, itself without colour, that can be transformed into a coloured compound, or can react with another material to form a coloured compound), or “colour base”. The other substance is an enzyme (a protein that acts as a catalyst in mediating and speeding a specific chemical reaction).
The distribution of pigmentation can be varied, inhibited or limited in extent. The interaction of chromogen and enzymes results in the formation of pigment granules known as melanin. Melanin is the substance responsible for all pigmentation in skin, eyes and hair etc.
Without melanin, mammals (including dogs) would appear totally albino (pale/translucent with a pink tinge – pinkness comes from the blood colour of the cells). Melanin is essential to all living beings because it protects the cells by trapping light rays & reduces the effects of ultraviolet radiation.
In the case of coat colour, melanin can be distributed in varying degrees and patterns in either or both the outside layer (cortex) or the inner (medulla) of each hair shaft. Variations in the process produces different optical effects resulting in the different coat colour varieties of dogs.
The colour of a cocker spaniels coat (fur) is controlled by chromosomes (a threadlike strand of DNA in the cell nucleus that carries the genes in a linear order). Each set of chromosomes is responsible for a particular physical characteristic, in the case of coat colour the “instruction” is carried on an Allele (one of the variant forms of a gene at a particular location on a chromosome.) When 3 or more alleles are found they are classified & arranged in the order in which they mask, conceal or cover the expression of the other members of the series.
As with all genetic traits every animal inherits one copy of each locus from each of its parents. Each of these loci is responsible for one or more traits either independently, or in conjunction with another locus. The appearance of a dog is known as its phenotype, the genetic makeup of the dog is known as its genotype.
In the cocker spaniel Black (in solid colours) and Blue Roan (in parti-colours) are the dominant colours (controlled by the genes for Black ‘BB’). All other colours are recessive to Black/Blue Roan.
In order for a dog to produce offspring in the coat colours that are Recessive, both parents need to carry for the recessive colour in question whether that is red/orange, liver/chocolate, orange/black/liver & white or recessive tan (any base colour with tan points). Recessive genes can appear to skip generations, however they are not truly skipping, being recessive, if they are overshadowed by a dominant gene at the same loci then their presence isn’t obvious & the recessive gene is carried (silently) forward onto the next generation in a proportion of offspring (as per Mendelian Inheritance).
It is often the case that either a Black or a Blue Roan can produce recessive coloured offspring when mated to a recessive coloured partner or a partner who carries recessive colours. In this instance, the dominant gene makes the dog look Black or Blue Roan but the hidden recessives are present & waiting to meet a recessive gene from the other parent, at the time of fertilisation the two recessives join to give rise to one or more recessive coloured offspring.
Dominant genes are traditionally represented by a capital letter; recessive genes are shown as lowercase letters. Therefore capital ‘B’ is for black, recessive brown (liver) is lowercase ‘b’. Each locus will have two genes, they could be two dominant genes – ‘BB’ or two recessives – ‘bb’ (both known as homozygous meaning the same) or the locus could have a heterozygous pair (dissimilar alleles at corresponding chromosomal loci) namely ‘Bb’. A dog carrying two copies of dominant ‘B’ will be black in colour and CANNOT produce liver coloured offspring regardless of the genes his partner carries.
A heterozygous dog carrying one dominant and one recessive – ‘Bb’ will be black in colour but will pass the recessive ‘b’ (liver) onto 50% of his offspring. The same principle applies to the other coat colour genes.
A recessive coloured dog – ‘ee’ (red) has no dominant gene (‘E’) to overshadow the recessive, therefore he will be red in colour and he will pass the recessive ‘e’ to all of his offspring – all offspring will carry for red (orange in the parti-colours). If he were heterozygous for ‘E’ i.e. ‘Ee’, he would be black in colour – the Dominant ‘E’ will mask its recessive partner (‘e’) however he will still pass recessive red (‘e’) onto 50% of his offspring.
Because coat colour is hereditary, the coat colour of puppies from a mating is determined on the coat colour genes carried by both parents, if however one parent is true Dominant (two dominant genes for a particular colour), the dominant gene will overshadow any recessive genes the other parent carries & although a proportion of the puppies will carry a recessive colour they will be the same colour as the Dominant parent.
For example, if an orange roan is mated to a liver roan, unless the orange carries for liver & the liver carries for orange, ALL puppies will be Blue Roan (as blue roan is the Dominant parti-colour), there will be no liver or orange roan puppies in the litter.
For Punnett squares showing predicted outcomes visit our colour combinations page.
Coat colour inheritance has been the subject of many studies, the researcher/author most relied upon is Clarence C Little. His book, “The Inheritance of coat colour in dogs” – Howell Book House 1976 forms the basis of the information which follows (new information is acknowledged).
The recognised colour series (loci – that is locations on the chromosomes) for coat colour in the cocker spaniel are:
A – (agouti, responsible for distribution of dark pigment and yellow pigment i.e. sable and tan ‘points’),
B – (black/brown),
C – (chinchilla series – responsible for full colour or pale colour),
D – (dilution of colour – separate from the chinchilla series),
E – (extension which is responsible for red colour & sable pattern in Cockers),
G – (greying),
K – (dominant black)
In most dogs including the Cocker Spaniel the main loci affecting coat colour are: ‘A’ (Agouti), ‘B’ (Black) & ‘E’ (Extension for red). Coat pattern will be discussed later – colour & pattern are two separate traits.
A: The Agouti series. This influences the location of dark pigment (black/brown) and of light pigment (yellow/tan) – there are at least three alleles in this series.
The ‘As‘ allele allows the distribution of dark pigment over the whole body surface (and used to be considered as Dominant Black) – it is now doubtful whether this allele actually exists – more recent studies indicate that KB is the gene responsible.
The ‘ay‘ allele restricts the areas of dark pigment and can produce a sable (looks red when the dog is ‘ay‘ay‘ unless the dog is shaded sable ‘ay‘at‘) or a tan individual (‘atat‘).
The sable gene in English Cocker Spaniels (according to VetGen) is not the same as it is for other breeds. It is located on the ‘E’ series.
The ‘at‘ allele produces ‘tan points’ i.e. bi-colour ‘X and tan’. The ‘tan’ allele can be modified by the ‘K’ series (dominant black), the ‘K’ alleles work with or against the ‘A’ loci and if inherited as a double dominant ‘Kb Kb‘ a dog cannot be ‘tan pointed’ and is not capable of producing ‘tan pointed’ offspring regardless of the effect of the ‘at‘ allele (due to Dominant Black Kb overriding the ‘at‘ alleles).
If inherited as a heterozygous pair i.e. ‘Kk’ the dog cannot be ‘tan pointed’ but it can give rise to ‘tan pointed’ offspring if the offspring are ‘at‘ and recessive ‘k’. Finally if inherited as a recessive homozygous pair i.e. ‘kk’ the dog will show ‘tan points’ if he also carries two copies of the ‘at‘ allele – all tan pointed dog have to have the recessive ‘kk’ also shown as ‘ky‘.
Some “tan pointed” dogs have bright clear tan; likely to be due to the ‘at‘at‘/’ky‘ky‘ alleles and others have a smokey tan, these are likely to be ‘at‘at‘/’ky‘. As the ‘K’ series modifies the depth of pigment those dogs with only one copy of ‘ky‘ are prevented from exhibiting full colour expression and their “tan points” are likely to be less pigmented (pale).
| Depth Of Pigment Due To The ‘A’ and ‘K’ Series | |
|---|---|
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| at at‘/’kk ky | at at‘/’ky ky |
The ‘aw‘ allele is not seen in Cocker Spaniels. It produces a ‘salt & pepper’ appearance like a wild Wolf. Clarence Little refers to this allele as the ‘wild type’.
| Colour Distribution Due To The ‘A’ Series | |||
|---|---|---|---|
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| As As Black |
at at Black & Tan |
As As RR Blue Roan |
at at RR Blue Roan & Tan |
It is worth mentioning that some dogs can be mistaken as carriers of ‘tan’ points due to ginger or pink fur appearing at various locations (generally the feet, around the eyes, around the mouth & the hind quarters, basically anywhere the dog can reach to lick themselves or where saliva or tears can collect). This is “porphyrin” staining and not tan.
When white or light coloured fur comes into contact repeatedly with saliva, it often turns pink or ginger. Porphyrin is a chemical found in saliva & tears. When the saliva dries on the coat, the porphyrin changes from transparent in colour to a pinkish brown. This can happen to all dogs with white in their coat & is especially evident on nursing bitches, the fur around their teats turns pink/ginger from the saliva from the nursing puppies!
B: The Black locus. This series is relatively straightforward as there are only two genes at this location and their interaction with the other alleles is known!
Dominant ‘B’, in single dose (‘Bb’) or double dose (‘BB’), allows the production of black pigment.
Recessive ‘b’ is dominated by dominant ‘B’, however in a double dose (‘bb’) produces brown (liver/chocolate) pigment wherever the dog would otherwise have produced black.
The ‘B’ gene appears to code for one of the proteins that makes up the eumelanin pigment granule. ‘B’ makes large deeply pigmented granules where as ‘bb’ granules are smaller and rounder in shape as well as appearing a lighter colour than those of a dog carrying ‘B’. The ‘B’ genes also have some effect on the iris of the eye and on the skin colour, including the eye rims and the nose leather. Phaeomelanin (yellow/tan) is not affected, so the colour of the tan points on for instance, a Black & Tan cocker isn’t affected by the ‘B’ genes. Dominant ‘B’ dogs will have dark eyes/nose; recessive ‘b’ dogs will have lighter (hazel) eyes and a brown nose.
| Eumelanin Distribution Due To The ‘B’ Series | |||
|---|---|---|---|
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| B B | B B | b b | b b |
The pigmentation responsible for black (“eumelanin”) can become faded or sun bleached with time. This happens to ‘old’ coat (fur) and can produce a brown or reddish ‘tinge’ or ‘cast’ to the coat especially when sunlight glints across the hairs. On blue roans & blacks the ‘tinge’ is brownish coloured. On Liver’s and Liver Roans the ‘tinge’ is more rusty coloured. In a Black or Blue Roan dog this is not an indication that the dog is carrying recessive liver (‘b’) it is simply aged coat which has lost some depth of pigmentation within the hair shaft. A dog may or may not be carrying recessive liver, but the faded appearance of what was once deep & dark due to pigmentation is no indicator.
E: The Extension series (also known as the melanocortin receptor 1). The ‘E’ series is responsible for the black mask seen in many breeds, and more significantly, for the presence of the yellow/red coat colour and sable pattern. The gene involved has at least four versions (alleles) affecting the appearance of the dog:
‘Em‘ – gives a dark mask (super extension) on ‘k’ recessives; otherwise allows for self coloured.
‘E’ – allows for self coloured dog; i.e. the actions of alleles on the ‘B’, ‘A’ and ‘K’ loci are expressed.
‘eh‘ is the sable allele.
‘ee’ – prevents eumelanin from being produced – dogs with two copies (homozygous) for ‘e’ will be yellow, orange or red in their pigmented coat.
The ‘E’ locus controls the extension of the two pigments in the hair follicle. ‘E’ is dominant and allows the extension of eumelanin, so the dog is black or brown. ‘e’ is the recessive form and allows the extension of phaeomelanin but prevents the extension of eumelanin, so there is no eumelanin in the pigment and therefore the animal is red (yellow).
‘Em‘ is the first gene in the series, however the gene isn’t seen in Cocker Spaniels (as far as I’m aware) , it is responsible for fawn dogs with black masks i.e. Pugs.
The ‘E’ series acts as modifiers to other genes: Recessive ‘ee’, overrides whatever gene is present at the ‘B’ and ‘A’ loci to produce a dog which shows only phaeomelanin (yellow) pigment in the coat. Therefore, for example, two orange roan (or solid red) cockers both carrying ‘ee’ (red) and carrying ‘b’ liver cannot produce solid liver or liver roan offspring. Dominant ‘E’ allows the genes at the ‘B’, ‘K’ and ‘A’ loci to be expressed & recessive ‘e’ overrides the ‘B’ loci.
If the ‘A’ alleles are dominant, i.e. ‘As’ the dog will have dark pigment (Black/Brown as determined by the ‘B’ genes) as the ‘E’ will allow the genes to express themselves (show through).
If however the ‘A’ alleles are the epistatic genes (the other genes in the sequence with ‘ay’ being the next dominant after ‘As’) the dog will have ‘ay’ at the ‘A’ locus. If there isn’t a dominant ‘As’ to counteract the recessive gene the coat will be tan (looks red) due to the dominant ‘E’ allowing the recessive ‘ay’ gene to show as it restricts dark pigment (eumelanin). This is how a red cocker can look red but in fact not have the double recessive ‘ee’ (red) genes.
| Colour Extension Due To The ‘E’ Series | |||||
|---|---|---|---|---|---|
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| Em Em | E E | eh eh | eh eh RR | e e | e e RR |
For most breeds the sable coat pattern is inherited in the same way. You need a sable gene ‘ay‘ combined with the tan gene ‘at‘ for shaded sable to occur (both ‘a’ genes are on the Agouti series). Shaded sable produces a coat pattern where the root of the hair is dark pigmented and the tips are golden/red.
For English Cocker Spaniels the genes responsible for sable are different to other breeds according to VetGen (opens a new browser window).
Dogs with homozygous alleles ‘eh‘eh‘ will be sable. When only one copy of the sable mutation is present, the dog will carry the mutation but may or may not express the pattern; this is because of the hierarchy of dominance. The sable mutation is recessive to ‘E’ and dominant to ‘e’, therefore if a sable carrying dog is also recessive red ‘e’ on the paired allele he will be sable, if however he is dominant red ‘E’ on the paired allele the dominant ‘E’ will prevent the sable pattern from being expressed.
| Sable Due To The ‘E’ Series | ||
|---|---|---|
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| N eh Clear Sable Solid |
eh eh Shaded Sable Solid |
eh eh RR Shaded Sable Roan |
Dominant ‘E’ can work with the other genes to mask a dogs ‘true’ colour. Because of its ability allow the expression of the genes in the ‘A’ series (‘As‘ allows dark pigment – black/brown & ‘eh‘ and ‘at‘ allows yellow pigment). If the dog is carrying the dominant ‘A’ he will have dark pigment (unless he is also ‘ee’ which will override the ‘A’ genes!), however if the dog is carrying the ‘eh”eh‘ genes he will appear to be solid red/orange roan, however he is not genotypically red (‘ee’), he will have either ‘Ee’ or ‘EE’ at that locus.
It is also possible for two genotypically ‘and tan’ dogs who appear phenotypically as Black dogs to produce offspring with ‘tan points’ as the dogs are true ‘and tan’ i.e. Black & Tan but the ‘E’ allele has restricted the appearance of the ‘tan’ – turned it so smoky black that it ‘disappears’ into the coat colour. The ‘Em‘ allele is thought to only affect the hair pigmentation and not the pigmentation to the nose and rims of the eyes (these will show the “hidden” colour).
Clarence Little was of the opinion that dominant Black was on the Agouti series, this hypothesis seems to have been disproved recently as new research by Dr. Sophile Candille and Dr. Christopher Kaeli (2007) (Stanford University School of Medicine) refer to the new ‘K’ gene. According to their research, the ‘K’ series comprise three alleles – KB, kbr, and ky as the genes associated with Dominant Black, Brindle and yellow (tan). Dr. Candille states “One version of the beta-defensin gene produces yellow dogs, a mutant version of the gene produces black.”
K: Dominant black series. KB has now been shown to be a critical allele in the formation of black pigment – dominant black (eumelanin) allele (gives a solidly dark black or brown dog.) If a dog has one copy of KB, the ‘B’ locus alone then determines whether the dog is black or liver. If the dog has one or two copies of ‘E’ and is therefore not ‘ee’, the ‘K’ loci will determine colour.
KBKB = self-coloured (solid colour in pigmented areas)
KBky = self-coloured (solid colour in pigmented areas)
kyky = allows expression of the ‘A’ agouti patterns
The ‘K’ alleles are beta-defensin’s (antimicrobial peptides) which apart from their antimicrobial properties now appear to have an influence on pigment. In dogs which have two recessive alleles ‘kk’, the ‘A’ series alleles are expressed – if you like the double ‘kk’ is like a clear window, it allows other colours and patterns, controlled by the ‘A’ series to show through.
‘ky‘ ‘ky‘ can express a variety of phenotypes – all dogs with tan points are ‘ky‘ in either a double or single dose provided they also carry double ‘atat‘. All fawn or sable dogs are also ‘ky‘ ‘ky‘, whether they have a melanistic (increased amount of black or nearly black pigmentation) mask or not. Red dogs that have an ‘ee’ genotype however, could be any genotype at the ‘K’ locus.
In order for any genes in the Agouti series to be seen the ‘K’ gene for pigment concentration must be expressed in a double recessive form of ‘ky‘ or ‘kk’ and dog with ‘kB‘ will not be ‘tan pointed’.
M (merle),
S (self coloured or modified S’ with S being dominant over the modified genes i.e. white spotting),
R (roaning),
T (ticking)
Cocker Spaniels have the base colours of black, brown and red, if the dog is a solid colour cocker the coat will show no pattern as a solid colour cocker is dominant for “Self” (depicted as a capital ‘S’ for a dominant gene) colour – see the ‘S’ series below.
S: The S series. The loci for self coloured is ‘S’. (self coloured or modified ‘S’ with ‘S’ being dominant over the modified alleles in the series) . Dogs with a dominant ‘S’ will be self coloured i.e. one colour (as determined by the other alleles) . The solid coat lacks pattern and is determined by the loci ‘S’, solid colour. This is the normal gene in breeds without white markings. An ‘SS’ dog can completely lack white, but it can also express very minor white markings such as a white streak on the chest.
Since ‘S’, solid colour is dominant, a solid can carry for parti-colour, but a parti-colour cannot carry for solid. A solid carrying two genes for solid (‘SS’) can only produce solid and bred to a parti-colour will only result in solid colour puppies, but all those puppies will be carriers for parti-colour. If a solid that carries a gene for parti-colour is bred to a parti-colour, some puppies will be solids and some will be parti’s, but all the solids will carry for parti-colour.
If a solid colour cocker carries a heterozygous pair on the ‘S’ series i.e. ‘Ssp‘ the dog will appear solid, there may however be some white areas due to the ‘sp‘ (piebald spotting) allele, this dog will probably be ‘mismarked’, the extent of the mismarking can be varied from barely noticeable to very obvious and is thought to be influenced by the ‘K’ series.
If the dog is a parti-colour he will have a modified ‘S’ allele in the form of “piebald” shown as ‘Sp‘ (this will give large unbroken areas of white to the coat as in “black & white”, “orange & white” or “liver & white”) and be double recessive for none roan ‘rr’. If the dog is a Roan, he will carry the gene responsible for the roan pattern i.e. ‘RR’ (homozygous) or ‘Rr’ (heterozygous).
An open marked dog will lack ticking or roaning in the coat. An open marked dog will have clear white between patches of darker colour. When ticking occurs between patches, they are not truly open marked but registered as the base colour, white, and ticked. Lack of ticking ‘tt’ is recessive to roan and ticking ‘TT’.
As mentioned, open marking (also know as “and white”) is controlled by the ‘S’ loci, more precisely thought to be the ‘Sp‘ allele which is epistatic (a dependent relationship between genes which results in a “hierarchy” between the genes), in the case of the ‘S’ loci the order of epistasis is ‘S’ followed by ‘Si‘, ‘Sp‘ & finally ‘Sw‘ – as seen in breeds such as the Bull Terrier, I have never seen a ‘Sw‘ cocker.
Therefore, technically an “and white” coat colour is a solid colour modified, i.e. a black and white cocker is effectively a black (BB) modified by a double ‘Sp‘ allele (which disables the body’s ability to make pigment i.e. white areas LACK pigment) to give a phenotype of Black and White. (Note that the ‘Si‘ and ‘Sw‘ genes also work in the same way). The ‘Si‘ allele gives rise to a parti-colour which has extensive areas of solid colour (very little parti-colour visible and normally on the undersides of the dog) but clearly a parti-colour as opposed to a Roan or Solid.
| Colour Distribution Due To The ‘S’ Series | |||
|---|---|---|---|
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| S S | si si | sp sp | sw sw |
R: The loci for the roan pattern is ‘R’, roan. The nature of the coat pattern and the progressive development of dark hair in a light area are unclear and is still in debate. Roan is defined as “having the base colour (as black, brown or red) muted and lightened by a mixture of white hairs.” Roan ‘RR’ appears to be dominant to ‘rr’ non-roan, i.e. open marks. Roan can carry for open marks, but open marks cannot carry for roan. For example, a Roan dog can carry for parti-colour (piebald) but a parti-colour (Black & White/Orange & White) cannot carry for Roan. Dark roan is generally thought to be dominant over light roan therefore two light roans should not be able to produce dark roan offspring. However it is perfectly possible for light roan to produce dark roans and it is thought that modifiers affect the extension ‘E’ colour.
| Colour Distribution Due To The ‘R’ Allele | ||
|---|---|---|
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| BB EE AA RR | BB ee AA RR | bb EE AA RR |
All ‘roan’ dogs will carry recessive solid i.e. ‘s’ on one allele, on the other allele they may also be recessive solid ‘s’ or they may have the epistatic piebald gene ‘sp‘ on the other. E.g. ‘BB’ (Black), ‘EE’ (not red or carrying red), ‘AA’ (not tan or carrying tan), ‘Aa’ (not tan but carrying tan), ‘aa’ tan, ‘ss’ (not carrying piebald) or ‘ssp‘ (carrying piebald) & finally either ‘RR’ (dominant roan) or ‘Rr’ (heterozygous roan).
T: The loci for the ticking pattern is ‘T’, ticking. Open marked colours may also have “ticking” in the coat. Ticking are flecks of colour in areas where the coat would have been white. When ticking occurs between patches, they are registered as X colour, white and ticked. ‘T’ (ticking) is dominant over ‘t’ lack of ticking. The amount and location of ticking are greatly affected by genes for size, shape and density of the ticking.
| Ticking Due To The ‘T’ Allele | ||
|---|---|---|
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| BB EE AA spsp rr TT | BB ee AA spsp rr TT | BB ee atat spsp rr TT |
As explained above coat colour (the genes controlling the pigment for coat colour) is inherited from the parents. Each parent will carry the genes responsible either as dominant or recessive genes.
Dominant genes are genes that produce the same phenotype (visible physical characteristic) in an organism whether or not its paired allele is identical (genes occur in pairs – one inherited from each parent!). Recessive genes are genes that produce their characteristic phenotype (visible physical characteristic) only when its paired allele is identical.
C: The albino series. ‘C’, allows full colour to develop, and is probably the structural gene for tyrosinase (an enzyme required to synthesize the black pigment melanin). ‘C’ is known to have a number of different forms and effects. The usual assumption is that dogs have at least one mutant allele, ‘cch‘ which when homozygous (two copies) lightens phaeomelanin (yellow) pigment to cream and more weakly affects liver and longhaired black. Another allele in the series is the ‘ce‘ (extreme dilution), this gives rise to a dog that is sufficiently pale to be almost white (pale cream) but will have pigmentation to the nose/eyes unlike a true albino which would have a pink (flesh) coloured nose and eyes.
In the case of cocker spaniels, Red (or orange in the parti-colours) can be seen as a deep rich red (almost Irish Setter red) to a pale gold (almost Golden Retriever gold), in the parti-colours Orange can be a deep rusty Orange (called Red Roan in the USA) or a pale cream (sometimes referred to as Lemon). The ‘C’ series is responsible for the variation, dogs exhibiting the deep colours are likely to be dominant ‘C’ whereas the paler colours are likely to have the recessive ‘cch‘ allele in a double dose as ‘C’ would override a single copy of the ‘cch‘ allele.
At its extreme form, ‘cc’, this series cannot produce working tyrosinase or melanin pigment due to the lack of tyrosinase and results in a white dog with pink eyes and skin.
| Colour (pigment) Dilution Due To The ‘C’ Series | ||||
|---|---|---|---|---|
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| CC | Cch | cch cch | Ce Ce | cc |
D: The dilution series. ‘D’ (dominant, full pigmentation) and ‘d’ (recessive, dilute pigment). Unlike the ‘C’ series ‘D’ affects both pigments (eumelanin – black/brown and phaeomelanin – yellow) whereas ‘C’ mainly affects phaeomelanin (yellow).
‘D’ is thought to act by causing the clumping of pigment granules in the hair. Like the ‘B’ alleles, it often affects skin and eye colour, ‘dd’ blacks will be described as “blue” and ‘dd’ liver dogs will be fawn (Isabella – Liver ‘bb’ diluted by the ‘dd’ alleles) as seen in Weimeraner’s and Dobermans. Dogs with dominant ‘D’ will be densely pigmented whereas dogs with recessive ‘d’ will be diluted. In addition to this, dogs carrying the ‘dd’ gene will have pale eyes (irises) and noses as the effect on the dilution of the pigment will occur in the skin as well as the coat.
| Eumelanin & Phaeomelanin Distribution Due To The ‘D’ Alleles | |
|---|---|
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| BB dd Solid Black with dilution |
bb dd Solid Liver with dilution |
As we do not see Blue (similar to the Blue Great Dane or a Blue Chow Chow) in the breed and neither do we see Fawn (similar to Pugs/Weimeraners) I have to assume that Cocker Spaniels are dominant for ‘D’. If there was a recessive dilution gene ‘dd’ in their genotype the dog would have a ‘washed out’/’faded’ appearance (sometimes referred to as “Silver Ash”). I don’t know if the gene appears in a heterozygous pairing though i.e. ‘Dd’, however at some stage the two recessive ‘d’s would come together to give offspring of ‘dd’ and to my knowledge this hasn’t occurred.
G: The greying genes. Clarence Little recognised only two genes in this series and the effect of the ‘G’ allele hasn’t been fully understood. It is believed that the effect of ‘G’, in single or double dose, is the replacement of coloured by transparent hairs as the animal ages, very much like premature greying in human beings. The process is thought to occur from birth so that as the dog ages the amount of grey hair increases. Grey hair occurs when melanin ceases to be produced in the hair root and new hairs grow in without pigment. In the Poodle the greying gene is thought to produce a silver effect to the coat, therefore a black Poodle would start to take on a black/silver appearance, as it gets older.
| Greying Due To The ‘G’ Alleles | |
|---|---|
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| BB EE spsp rr Gg | BB Ee Ssp Rr Gg |
Over the years, I’ve had two dogs become grey at a young age (about 18 months old). One was a Black & White bitch, the other a Steel Blue Roan Dog. With the Black & White bitch the dark areas on her body remained jet black and only her ears/head turned silvery grey. The Steel Blue Roan dog did however; grey all over i.e. the body became more ‘silvery’. Both dogs had offspring whose black areas remained jet black until they passed away at a good age. This would mean that the dogs who greyed were ‘Gg’ genotype and those that stayed fully pigmented for life would have been recessive ‘gg’ meaning no greying. This effect of this gene must not be confused with the ‘salt & pepper’ style greying (especially around the muzzle) of dogs as they get very much older – it is natural for some grey to appear in older dogs!
I’m not sure the exact effect the ‘G’ alleles have on the coat of a cocker, from my own observations I am assuming there are other genes acting as modifiers.
M: The merle gene. Merle is a gene that gives both a pattern and has an affect on pigment. The ‘M’ gene dilutes pigment; it lightens whatever the coat colour would otherwise have been (Black becomes a grey dapple and Liver a brown dapple). Unlike the recessive ‘d’ dilution gene (which lightens the entire coat), Merle gives a patchy appearance. The effect of the lightening is not spread evenly over the coat, but leaves patches of undiluted colour scattered over the dog’s body giving a dappled appearance. The dominant gene is ‘M’ meaning merle, the recessive ‘m’, none merle. An ‘Mm’ dog is merle patterned due to the dominant ‘M’, but an ‘MM’ dog has much more white than is normal for the breed.
| Merle Due To The ‘M’ Alleles | ||
|---|---|---|
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| BB EE AA MM | BB EE AA Mm | bb EE AA MM |
In the case of cocker spaniels (English) the merle gene doesn’t seem to apply, to my knowledge there have been no merle cocker spaniels bred (it is worth noting that it’s possible genetically merle individuals have been mistaken for roans although eye colour should have been diluted to blue). I’ve not seen or heard of any adult blue roan dogs with blue irises so I assume there are no Merle English Cockers. Merle’s do seem to occur in American Cocker Spaniels in the USA, although breeders of Merle American Cockers have recently recognised the health implications associated with the Merle pattern and their popularity may be in decline.
Heterozygous merle’s ‘Mm’ appear to be free of congenital defects associated with the colour, however many homozygous merle’s ‘MM’ are known to have health issues including deafness, blindness, gastrointestinal problems and many are sterile. In some cases, many of the offspring (carrying the double ‘MM’) will have so many congenital/developmental defects that they are incompatible with life and will either be stillborn or die shortly after birth.
Homozygous Merles ‘Mm’ will generally have pigment around the head/ears etc. where as Dominant heterozygous Merle’s ‘MM’ will have a lot of white in the coat including over the head/ears, it is generally thought that white headed dogs are at most risk of deafness and/or blindness. With Merle dogs, deafness is neither caused by dominant nor recessive genes, but is linked to a dominant gene that disrupts pigmentation and secondarily can cause deafness in the process.
Deafness occurs due to the suppression of melanocytes (pigmentation cells) in the the vascular bed in the cochlea (the spiral cavity of the inner ear containing the organ of Corti, which produces nerve impulses in response to sound vibrations). This suppression causes degeneration of the tissue which in turn leads to death of the hair cells in the cochlea. These hair cells are responsible for detecting sound as they pick up the vibrations from the tiny bones in the ear and transmit the vibrations to the brain to be interpreted into sound.
Merle does not express itself fully without eumelanin (dark pigment), which means that solid reds/orange roans could be genetic merles and not appear any different from genetically ‘ee’ dogs. Therefore, although the Merle pattern doesn’t appear to occur in Cockers it is imperative that any dog suspected as being Merle is not bred to a solid red/orange roan or indeed another Merle to avoid the risk of producing double ‘MM’ offspring and therefore avoid the risk of producing offspring with health issues.
It is common for most if not all young puppies to have “blue” eyes, that is to say that in certain lights a pups eyes can appear to be similar to navy blue rather than the deep brown colour normally associated with most breeds of dog.
The dark brown colour of dog’s eyes is produced by ‘eumelanin’ (as with coat colour). Whilst a puppy is young & immature, the pups body hasn’t finished distributing this pigment yet. Over the first weeks/months of life, as the pups eyes develop (usually by 10 -12 weeks of age) and their bodies produce more eumelanin (dark pigment), the irises gradually change from “blue” to their permanent colour (brown, deep brown or hazel – as determined by the ‘B’ alleles).
Until the irises are fully pigmented an immature pups eyes will appear ‘blue’. Blue is the most easily “scattered,” or reflected, colour of light in the spectrum (it is nature’s “default” colour). Immature irises (which do not really reflect any colour as they lack pigmentation) will appear ‘blue’ until the irises are fully pigmented with melanin (which will give the dark pigmentation to the iris).
Therefore, it can be assumed that young dogs with “blue” eyes are not Merles unless of course there are other indicators of Merle colouring. If a puppy is genetically Merle, the “blue” eye colouring will NOT (as the puppy matures) turn brown because the Merle gene DILUTES pigment, therefore the eumelanin (dark pigment) is diluted and the eyes appear ‘blue’ indefinitely – normally a brighter blue than navy.
If the S-locus is ‘S’, the coat, nose & feet pads will be fully pigmented (colour as defined by the other alleles).
If the S-locus is heterozygous ‘Ssp‘ the coat will be fully pigmented, however small areas of white may appear making the dog ‘mismarked’.
If the S-locus is ‘sp‘, the coat, nose and feet pads will be piebald (X ‘and white’ – as controlled by the ‘B’ and ‘E’ alleles)
If the R-locus is ‘RR’ the coat will be Roan unless the dog has a dominant ‘S’ for solid.
If the T-locus is ‘TT’ the coat will have ticking unless the dog has dominant ‘R’ for Roan or dominant ‘S’ for solid.
If the B-locus is ‘B’, the coat will be black UNLESS the dog is also ‘ee’ where the coat will be red.
If the B-locus is ‘bb’, the nose and coat will be brown UNLESS the dog is ‘ee’ where the dog will be red with a brown nose and pads.
If the E-locus is ‘ee’, the coat is ALWAYS red. ‘ee’ is epistatic (suppresses the effect of a gene at another locus) to both the ‘A’ and the ‘K’ locus.
If the E-locus is ‘EE’ or ‘Ee’ and if it is ‘K’ at the ‘K’ locus its coat will be entirely eumelanin based (dominant black).
If the E-locus is ‘EE’ or ‘Ee’ and if it is ‘kk’ at the ‘K’ locus the distribution of eumelanin and phaeomelanin will be determined solely by the Agouti alleles present.
If the K-locus is ‘K’ the coat will be dark in colouration (as determined by the ‘B’ loci) – dominant ‘K’ is epistatic (overrides) the ‘A’ series, however double recessive ‘ee’ is not affected by the dominant ‘K’ as no dark pigment can be produced.
If the K-locus is ‘kk’ the coat will be coloured according to the ‘A’ series, as recessive ‘kk’ allows the ‘A’ series to express itself.
If the A-locus is ‘As‘ the dog will have dark pigment over the whole body surface – one dominant copy overrides any other ‘A’ series alleles.
If the A-locus is ‘ayay‘ the dog will be clear sable (red).
If the A-locus is ‘atat‘ the dog will have ‘tan points’, the alleles for ‘B’ and ‘E’ are not affected.
Therefore ALL dogs with tan points (‘at‘) are ‘kk’. Likewise, ALL dogs whose red colour is caused by ‘ay‘ and not ‘ee’ are also ‘kk’. No ‘ayay‘ dogs have the black tips at the ends of the hairs because their ‘ee’ genotype prevents the production of dark pigment.
Without a test mating it can be difficult to know if a red dog is true red ‘ee’ or red due to ‘ayay‘ however, true reds will have pale whiskers (no black can be produced) and clear sables (looking red) will generally have dark whiskers due to a copy of dominant ‘E’ allowing the extension of eumelanin (black/brown).
DOMINANT genes will overshadow the effect of their recessive counterpart (in the same series) however dominance can be complete or incomplete which means that some Dominant genes can overshadow the dominant genes in other locations.
Whilst I was writing this article I had to think firstly about colour genetics and secondly about the page construction (code) – two reasonably complex tasks! If you find any errors in the theory or coat colour combinations I’d be very grateful if you could let me know!