Understanding Bull Terrier Coat Color Genetics and Inheritance

Bull Terriers are classified as either "white" or "colored." While a white Bull Terrier can appear to be completely white they always carry a color, even you do not see any markings. On a white Bull Terrier markings (of color) are permissible on the head only.

White Bull Terriers

White: all white.
White and brindle: head markings that are variation of red brown to a dark mahogany with an even darker color that can look like tiger striping or marbling.
White and black brindle: head markings that are black with light colored brindling (often making it challenging to discern between a black brindle marking and a black/tan marking).
White, black and tan: head markings that are black and tan without marbling found in the black brindle markings.
White and fawn: head markings are a lighter, faded red (also sometimes accompanied by the dark black smut hairs)

Colored Bull Terriers

Brindles can range from a base of very dark brown (mahogany brindle) to more of a red (red brindle) to a tan (fawn brindle) to a very pale fawn (silver brindle).

Brindle: often referred to as a solid brindle the dog's body will be a variety of brown striping with only small bits of white found: occasionally as a snip of white above the nose, on the chin, tips of the paws, chest and maybe some on the belly. Can sometimes have a darker mask on the muzzle and eyes like the “smuts” described below.
Brindle and white: brindles with a blaze of some sort of white on the head, white on the legs down to feet, a white chest that often wraps around the neck, a white belly and a white tip on the tail.
Black brindle: often referred to as a solid black brindle the dog is primarily black with brindling located on the cheeks, chest, behind the elbows, the flanks and under the tail. Occasionally there is a snip of white above the nose, on the chin, tips of the paws, chest and maybe some on the belly.
Black brindle and white: black brindles with a blaze of some sort of white on the head, white on the legs down to feet, a white chest that often wraps around the neck, a white belly and a white tip on the tail. The brindling is often found in the areas where the black meets the white.

Reds can range in color from a deep red to more of an orange but are distinct in their depth of coat color from the Fawns who have a sandy, tan colored coat.

Red: often referred to as a solid red the dog's body will be red with only small bits of white found: occasionally as a snip of white above the nose, on the chin, tips of the paws, chest and maybe some on the belly.
If the animal also has black masking on the muzzle and eyes and black hairs found through the body with a concentration on the tail this is referred to as smut and the animal would be categorized as a “red smut”.
Red and white: reds with a blaze of some sort of white on the head, white on the legs down to feet, a white chest that often wraps around the neck, a white belly and a white tip on the tail. If the animal has the smut masking it would be a red smut and white.

Tricolors (black, tan and white) and the black brindles can sometimes be confused for one another.

Black and tan: primarily black with tan located on the cheeks, chest, behind the elbows, the flanks and under the tail. Occasionally there is white present although these animals are not referred to as tri color. The white can be found as a snip above the nose, on the chin, tips of the paws, chest and maybe some on the belly.
Black, tan and white (also known as Tri Color): a black coat with a blaze of some sort of white on the head, white on the legs down to feet, a white chest that often wraps around the neck, a white belly, white tip on the tail and tan marks located on the cheeks, chest, behind the elbows, the flanks and under the tail.

Color In Bull Terriers

Expression of Colour

There are a limited number of coat colours in Bull Terriers. All Bull Terriers fall into one of two groups:

there is the iconic White Bull Terrier which is either all white or may have small patches of colour, and the Coloured Bull Terrier which, while it may have some white markings, is predominantly coloured - either Brindle, Red, Black & Tan or Black Brindle.

In order to understand coat colour in Bull Terriers it is only necessary to know that there are three sets of genes causing these colour varieties. In a simplified way, they are:

Base Coat Colour gene (known as the Agouti- or A-Locus Series)
This gene causes two options:
Red Base Coat –

This is a plain red base coat (seen in a Red dog or found under the brindle pattern of a Brindle dog). The plain red base coat can vary from light tan through to a deep red brown.

Black on Red Base Coat –

This is a black overcoat on the red base coat (seen in a Black & Tan/Tricolour dog or under the brindle pattern of a Black Brindle dog). The black overcoat on the red base coat will be referred to here as Black on Red and is essentially a black covering on the red base coat. This black covering does not fully extend over the red and the red colour can be seen on the face forming eyebrows and cheek patches, on the chest, lower legs and under the tail. The extent of red showing around the edges of the black varies in individual dogs.
Brindle Patterning gene (known as the K-Locus Series)

This gene causes two options:
No Brindle Pattern –

This is seen in Red dogs and Black & Tan/Tricolour dogs.

Brindle Pattern –

Brindle is a pattern of black stripes on the background colour of the base coat.

The brindle pattern on the Red base coat shows as a Brindle dog and the brindle pattern on a Black on Red base coat shows as a Black Brindle dog. Variation in the shade of colour of the base coat and the width of the black stripes can result in unique brindle patterns.
White Masking gene (known as the S-Locus Series)

This gene controls the amount of white pattern masking the colour of the dog. A complete white mask results in a White Bull Terrier.

It is important to realise that a White Bull Terrier has got colour (a Red or Black on Red base coat and a Brindle pattern or not) like any Coloured Bull Terrier. The white mask is simply covering it and preventing it from being visible.

The white mask pattern may not cover the whole dog. It may cover part of the face, throat, neck and chest, much of the under-body, the lower legs and the tip of the tail. This results in a Coloured & White Bull Terrier (white should only cross the back of the dog at the neck).

A Bull Terrier with no white markings or very limited white patches without any extension over the back at all is a Solid Coloured Bull Terrier.

In Bull Terriers, a less important fourth gene (MC1R gene) is responsible for the dark facial mask known as smut marking. Up until 2007, it was believed that only Red Bull Terriers could have smut markings and that Brindle, Black Brindle and Black & Tan/Tricolour Bull Terriers did not have this at all. We now know that all Coloured Bull Terriers can have smut markings. It is only is Red Bull Terriers that the mask is easily visible. In the other Coloured and White Bull Terriers the mask is either camouflaged by dark brindle patterning, hidden by the Black on Red base coat or covered by the white mask.

The different genetic combinations produce the following coat colour options in Bull Terriers:
1. White – These appear all white but they may have patches of colour, most likely on the head near the ears and eyes. They are, however, not really white as all White Bull Terriers carry colour and pass on colour to their offspring even though that colour may not be visible. The White expression is a ‘mask’ hiding the true genetic colour of the dog. A careful look at the hairs around the ears of an all-White Bull Terrier can help figure out what colour it is carrying.
2. Red -This colour ranges from light tan through to deep, dark, rich, rust red. The colour “fawn” is a very pale version of this. Fawn colour is caused by the same gene as Red colour but the difference in expression is due to the rufous polygenes which, when inactive, result in a so-called ‘cold’ colour. There are different varieties –
  
  Red Solid - red with hardly any white markings – it might have a small white blaze on the nose, patch on the chest and white on the toes
  
  Red & White - red with strong white markings on the nose, collar, chest, underbelly, lower legs and feet and tail tip.
  
  Red Smut - red with a visible dark mask on the face and tip of the tail
  
  Clear Red - red with no dark mask on the face or tail
3. Brindle – This is a pattern of fine black lines superimposed on a variable red/fawn base colour producing a wide range of colours – gold brindle, silver brindle, red brindle and from light to dark brindle. There are two varieties –
  
  Brindle Solid – brindle with hardly any white markings – it might have a small white blaze on the nose, patch on the chest and white on the toes
  
  Brindle & White – brindle with strong white markings on the nose, collar, chest, underbelly, lower legs and feet and tail tip.
4. Black and Tan/Tricolour –This pattern is black with tan (red) markings on the eyebrows, cheeks, chest, lower legs and bottom. If minimal white is present, it is called a Black & Tan Solid (also known as Tricolour Solid) but if there is black and tan colouring with white markings on the face, collar, chest, underbelly, feet and tail, then it is called Black & Tan & White or, more commonly, is it simply called Tricolour (it is not a Solid).
5. Black Brindle –This pattern is black with brindled markings on the eyebrows, cheeks, chest, lower legs and bottom. The brindle colour can be very variable. If minimal white is present, it is called a Black Brindle Solid but if there is black and brindle colouring with white markings on the face, collar, chest, underbelly, feet and tail, then it is called Black Brindle & White.

General Rules of Colour Expression in Bull Terriers:

There are only three different genes causing colour variation in Bull Terriers.
These genes affect:
- the extent of white;
- the base coat colour and
- the brindling pattern.
This results in nine colour variations in Bull Terriers:
- White
- Brindle Solid
- Brindle & White
- Red Solid
- Red & White
- Black & Tan Solid (also known as Tricolour Solid)
- Tricolour (also known as Black & Tan & White)
- Black Brindle Solid
- Black Brindle & White

Inheritance of Colour

What coat colours are producing in different matings? Let us look at each gene separately first.

Inheritance of the White Mask

Any Bull Terrier will be one of three genetic options as far as the White Mask is concerned:

White – that is the body all white with or without coloured head markings
Coloured & White – predominantly coloured (not white) with strong white collar crossing the back, white chest, under-body, muzzle, blaze and feet
Solid Coloured – all Coloured with or without limited white markings on the muzzle, chest and/or feet

↓♀♂→	White	Coloured & White	Solid Coloured
White	100% White	50% White 50% Coloured & White	100% Coloured & White
Coloured & White	50% White 50% Coloured & White	25% White 50% Coloured & White 25% Solid Coloured	50% Coloured & White 50% Solid Coloured
Solid Coloured	100% Coloured & White	50% Coloured & White 50% Solid Coloured	100% Solid Coloured

Inheritance of the Base Coat Colour

Any Bull Terrier will be one of three genetic options as far as the Base Coat Colour is concerned:

True Red -
as in the Red Bull Terrier or Brindle Bull Terrier that has no parents nor grandparents that are Black & Tan/Tricolour or Black Brindle
Red carrying Black on Red -this Bull Terrier looks Red or Brindle but carries the gene to produce Black on Red colour as well as Red. This dog will have either a parent or a grandparent which is Black & Tan/Tricolour or Black Brindle
Black on Red -as in the Black & Tan/Tricolour and Black Brindle Bull Terriers

↓♀♂→	True Red	Red carrying Black on Red	Black on Red
True Red	100% Red	100% Red	100% Red
Red carrying Black on Red	100% Red	75% Red 25% Black on Red	50% Red 50% Black on Red
Black on Red	100% Red	50% Red 50% Black on Red	100% Black on Red

Inheritance of the Brindle Pattern

Any Bull Terrier will be one of three genetic options as far as the Brindle Pattern is concerned:

True Brindle -this Bull Terrier has brindle pattern on a red base coat appearing as a Brindle dog or it has the brindle pattern on a Black on Red base coat where just the red parts are brindled as in the case of Black Brindle dog. This dog has both Brindle parents and grandparents
Brindle carrying No Brindle Pattern -this dog is Brindle or Black Brindle as described above but it has a non-Brindle parent or grandparent (i.e. Red or Black & Tan/Tricolour)
No Brindle Pattern -the dog is either Red or Black & Tan/Tricolour with no sign of any brindle pattern

↓♀♂→	True Brindle	Brindle carrying No Brindle Pattern	No Brindle Pattern
True Brindle	100% Brindle	100% Brindle	100% Brindle
Brindle carrying No Brindle Pattern	100% Brindle	75% Brindle 25% Not Brindled	50% Brindle 50% Not Brindled
No Brindle Pattern	100% Brindle	50% Brindle 50% Not Brindled	100% Not Brindled

If a dog is White and the colour they are carrying is discernible, then the colour probabilities of the offspring can be predicted by using that known colour in these colour charts.

It must be highlighted that the actual proportions of the different colours presented in these tables will only be evident with very large numbers of puppies as a single litter of puppies is too small statistically to reflect this.

General Rules of Colour Inheritance in Bull Terriers:

Two White parents always produce all White puppies. These White puppies may have coloured marks on their heads but they will always be almost all White in colour. Two White parents cannot produce a predominantly Coloured puppy.
A White parent can never produce a Solid Coloured puppy – it can only produce a Coloured & White or an all White puppy.
A Solid Coloured parent will never produce an all White puppy. Even with a White mate, a Solid Coloured parent will produce Coloured & White puppies but never all White.
Two Solid Coloured parents will produce all Solid Coloured puppies.
A Solid Coloured parent and a White mate will produce all Coloured & White puppies.
A Solid Coloured parent and a Coloured & White mate can produce Solid Coloured and Coloured & White puppies (with a one in two chance for either).
A Coloured & White and an all White parent can produce White puppies and Coloured & White puppies (with a one in two chance for either).
In fact any Coloured & White parent has a one in two chance of producing Coloured & White puppies no matter what colour the mate is.
Two Coloured & White parents have a one in four chance of producing Solid Coloured puppies, a one in four chance of producing all White puppies and a two in four chance of producing Coloured & White puppies.
Brindle puppies will only result when either one of the parents is Brindle or White carrying Brindle. If a dog has a Brindle gene, they will show Brindle (either Brindle, Brindle & White, Black Brindle or Black Brindle & White) and only then can they pass Brindle on to their offspring. The only exception to this is if it is a White dog carrying that Brindle without any coloured marks to show it.
Two non-Brindle parents can never produce a Brindle puppy.
If Black & Tan Solid, Tricolour, Black Brindle Solid or Black Brindle & White dogs are bred with each other, the offspring will only be one of these four options.

By Tracey Butchart
Illustrations by Duncan Butchart

Coat Color In Bull Terriers

COLOUR IN BULL TERRIERS – Part 2 – Inheritance of Colour – Short Version

As discussed in “Colour in Bull Terriers – Part 1 –Expression of Colour”, the colours and colour patterns we observe in Bull Terriers are created by the interactions of just four genes. A restricted gene pool and selective breeding have removed the effect of the ten other coat colour genes for dogs in the Bull Terrier breed. Just as a reminder, there are 14 loci – particular locations on specific chromosomes where genetic material influencing coat colour can be found. The loci that are identical in all Bull Terriers are:

The B-Series Locus – Black/Brown Pigment Series

All Bull Terriers are believed to have the genotype BB i.e. they have black pigment of the nose, eye rims and mouth.

The C-Series Locus – Pigment Depth or Albino Series

All Bull Terriers are believed to have the genotype CC i.e. they have full colour expression with no dilution.

The D-Series Locus – Pigment Density Series

All Bull Terriers are believed to have the DD genotype resulting in normal pigment density and no dilution.

The G-Series Locus – Progressive Greying Pattern

All Bull Terriers are believed to have the genotype gg i.e. no progressive greying pattern is exhibited.

The P-Series Locus – Pigment Dilution

All Bull Terriers are believed to be PP which means that both melanin pigments are not diluted at all.

The I-Series Locus – Intensity Dilution

All Bull Terriers are believed to be II i.e. intense colour with no dilution of the phaeomelanin pigment.

The M-Series Locus – Merle Pattern

This locus has no effect in Bull Terriers as all Bull Terriers are believed to be mm – no merle pattern.

The H-Series Locus – Harlequin Pattern

The H allele is only expressed if the M allele causing the merle pattern is also present. As all Bull Terriers are mm for no merle pattern, so they are also hh for no harlequin pattern.

The T-Series Locus – Ticking Pattern

As ticks are a fault as laid out in the Standard of the Bull Terrier, this phenotype has been selectively bred out. All Bull Terriers should have the tt genotype with no ticking.

The R-Series Locus – Roan Pattern

Roan often occurs in dogs which also show ticking. Future research may reveal that it is a variation of ticking rather than a separate pattern. At present, Bull Terriers are believed to be rr i.e. no roan pattern. Remember genotype is the combination of alleles the dog possesses while its phenotype is what it actually looks like. Thus all Bull Terriers for these loci should have the following genotype: BBCCDDgghhIImmPPrrtt. Of course in all of these loci, mutation of a gene could, and does occur, causing a change from these genotypes. However as mutation is a random occurrence, it should not have any influence on the overall Bull Terrier population especially when selective breeding against these traits is being exercised. The four loci which cause variation in colour in Bull Terriers are:

The A-Series Locus – Dark Pigment Pattern or Agouti Series

While there are six alleles possible in the A-Series loci, only two of these occur in the Bull Terrier breed. These two alleles are Ay and at. Ay is completely dominant over at. This results in three genotypes and their corresponding phenotypes: Ay Ay – causing a red/fawn phenotype; Ay at – causing a darker red/fawn colour; at at – black and tan pattern. Basically there are two base coat options for a Bull Terrier: the red/fawn colour or a black pattern over the red/fawn colour where the red/fawn colour is visible as marks on the eyebrows and cheeks and edging the black on the chest and lower legs and on the bottom under the tail.

The K-Series Locus – Brindling Pattern

While there are three alleles possible in the K-Series loci, only two of these occur in the Bull Terrier. These two alleles are kbr and ky where kbr is dominant to ky. This results in three genotypes and their corresponding phenotypes: kbr kbr – A-Series colour with brindling pattern on the tan/sable; kbr ky – A-Series colour with brindling pattern on the tan/sable; ky ky – A-Series colour with no brindling pattern at all. As the kbr allele is dominant, if a Bull Terrier has this allele, it will display the brindle pattern and can pass on the brindle pattern. The only exception is in a white Bull Terrier carrying the kbr allele, which can pass on brindle but doesn’t display it due to the white mask.

The E-Series Locus – Pigment Extension

While there are three alleles possible in the E-Series loci, only two of these occur in the Bull Terrier. These two alleles are E and Em where Em is dominant over E. This results in three genotypes and their corresponding phenotypes: EE – Solid colour as defined by A-Locus Series – no dark mask; EEm – Colour as defined by A-Locus Series but with a dark mask; EmEm – Colour as defined by A-Locus Series but with a dark mask. Originally the brindle markings were believed to be controlled by the E-Series but now it has been found that the E-Series is only responsible for the black mask being present or absent in Bull Terriers. The mask causes darker colour on the muzzle mainly extending up towards the eyes and sometimes visible on the top of the back and tail and is known as smut marking. Before a dog could either be brindle or smut but not both. With the discovery of the K-Series controlling brindle patterns, brindle dogs (in fact any colour) can also have smut markings even if they are not visible due to the dark overall colour. This gene is a difficult one to consider as the dark mask is only really properly visible in Red Solids (and Fawn Solids) causing Red Smut and Fawn Smut. In Red and White and Fawn and White dogs (and even in Brindle and White), the mask is covered by the white facial patches and can only be visible as black lip markings or black tear marks. In Brindle and Black and Tan colours, the dark mask is not seen unless in the case of Brindle, the Brindle colour is very pale. The back facial mask may be much more common than it appears to be.

The S-Series Locus – White Spotting Pattern

While there are four alleles known to occur in the S-Series loci, it is speculated that only two of these occur in the Bull Terrier. They are si and sw with si dominant over sw. This results in three genotypes and their corresponding phenotypes: si si – Little or no white confined to the blaze, chest and feet – known as a Solid-Coloured; si sw – White blaze, chest, collar, underbelly, lower legs, feet and tail tip with white only extending over the back at the neck – known as Coloured & White; sw sw – All white – may have some colour markings confined to the head. Bull Terriers are believed to only have the alleles si and sw and not the dominant S allele that causes true solid colour. This idea may change with more research. There definitely is the occurrence of a Bull Terrier who appears solid coloured (with limited white markings) producing all white puppies (thereby proving it is not solid-coloured genetically), and the occurrence of a coloured dog with quite significant white markings unable to produce a white puppy (indicating that it is solid-coloured genetically). Plus and minus modifiers also act on this gene changing the way it is expressed. Putting these four loci and their different possible allele combinations together there are 27 different genotype options which would describe the 12 different phenotypes observed in Bull Terriers. Remember dominant alleles can mask the effect of a recessive allele so you can have two dogs which are phenotypically the same e.g. black brindle solids but genotypically they can be different e.g. at at kbr kbr si si and at at kbr ky si si. All possible genotype options for an observable phenotype have been included in the tables below. For simplification, it has been decided to leave out the effect of the E-Series locus as the effects of this are not visible in most of the phenotypes.

WHITE BULL TERRIERS

Phenotype	Option	Genotype	Possible Offspring Colours
White carrying Red/Fawn	1 2	Ay Ay ky ky sw sw Ay at ky ky sw sw	can produce WHITE, RED & WHITE and BRINDLE & WHITE puppies depending on the colour of the mate. can produce TRICOLOUR and BLACK BRINDLE & WHITE puppies as well as all WHITE, RED & WHITE and BRINDLE & WHITE depending on the colour of the mate.
White carrying Brindle	1	Ay Ay kbr kbr sw sw	- can only produce all WHITE and/or
			BRINDLE & WHITE puppies no
			matter what the colour of the mate.
	2	Ay Ay kbr ky sw sw	- can produce all WHITE, BRINDLE
			& WHITE and RED & WHITE
			puppies depending on the colour of
			the mate.
	3	Ay at kbr kbr sw sw	- can produce all WHITE, BRINDLE
			& WHITE and BLACK BRINDLE &
			WHITE puppies depending on the
			colour of the mate.
	4	Ay at kbr ky sw sw	- can produce all coloured & white
			options – BRINDLE & WHITE,
			BLACK BRINDLE & WHITE, RED & WHITE & TRICOLOUR as well as all WHITE puppies depending on the colour of the mate.

Phenotype	Option	Genotype	Possible Offspring Colours
White carrying Black & Tan	1	at at ky ky sw sw	- can produce all coloured & white options – BRINDLE & WHITE, RED & WHITE, BLACK BRINDLE & WHITE & TRICOLOUR as well as all WHITE puppies depending on the colour of the mate.
White carrying Black Brindle	1	at at kbr kbr sw sw	- can produce all WHITE, BRINDLE & WHITE or BLACK BRINDLE & WHITE depending on the colour of the mate.
	2	at at kbr ky sw sw	- can produce all coloured & white options – BRINDLE & WHITE, BLACK BRINDLE & WHITE, RED & WHITE & TRICOLOUR as well as all WHITE puppies depending on the colour of the mate.

RED BULL TERRIERS

Phenotype	Option	Genotype	Possible Offspring Colours
Red/Fawn Solid	1	Ay Ay ky ky si si	- can produce RED SOLID, BRINDLE SOLID, RED & WHITE and BRINDLE & WHITE puppies depending on the colour of the mate.
	2	Ay at ky ky si si	- can produce all solid coloured and coloured & white options – BRINDLE SOLID, BRINDLE & WHITE, RED SOLID, RED & WHITE, BLACK BRINDLE SOLID, BLACK BRINDLE & WHITE, BLACK & TAN SOLID and TRICOLOUR puppies depending on the colour of the mate.
Red/Fawn & White	1	Ay Ay ky ky si sw	- can produce RED SOLID, BRINDLE SOLID, RED & WHITE, BRINDLE & WHITE and all WHITE puppies depending on the colour of the mate.
	2	Ay at ky ky si sw	- can produce all colour options – BRINDLE SOLID, BRINDLE & WHITE, RED SOLID, RED & WHITE, BLACK BRINDLE SOLID, BLACK BRINDLE & WHITE, BLACK & TAN SOLID, TRICOLOUR and all WHITE puppies depending on the colour of the mate.

BLACK & TAN/ TRICOLOUR BULL TERRIERS

Phenotype	Option	Genotype	Possible Offspring Colours
Black & Tan Solid	1	at at ky ky si si	- can produce all colour options except WHITE – i.e. BRINDLE SOLID, BRINDLE & WHITE, RED SOLID, RED & WHITE, BLACK BRINDLE SOLID, BLACK BRINDLE & WHITE, BLACK & TAN SOLID and TRICOLOUR puppies depend- ing on the colour of the mate.
Tricolour	1	at at ky ky si sw	- can produce all colour options – BRINDLE SOLID, BRINDLE & WHITE, RED SOLID, RED & WHITE, BLACK BRINDLE SOLID, BLACK BRINDLE & WHITE, BLACK & TAN SOLID, TRICOLOUR and all WHITE puppies depending on the colour of the mate.

BRINDLE BULL TERRIERS

Phenotype	Option	Genotype	Possible Offspring Colours
Brindle Solid	1	Ay Ay kbr kbr si si	- can only produce BRINDLE
			SOLID and/or BRINDLE &
			WHITE puppies no matter what
			the colour of the mate is.
	2	Ay Ay kbr ky si si	- can produce BRINDLE
			SOLID, RED SOLID, BRINDLE
			& WHITE or RED & WHITE
			puppies depending on the
			colour of the mate.
	3	Ay at kbr kbr si si	- can produce BRINDLE
			SOLID, BLACK BRINDLE
			SOLID, BRINDLE & WHITE or
			BLACK BRINDLE & WHITE
			puppies depending on the
			colour of the mate.
	4	Ay at kbr ky si si	- can produce all colour options
			except WHITE – i.e. BRINDLE
			SOLID, BRINDLE & WHITE,
			RED SOLID, RED & WHITE,
			BLACK BRINDLE SOLID,
			BLACK BRINDLE & WHITE, BLACK & TAN SOLID and TRICOLOUR puppies depend- ing on the colour of the mate.

Phenotype	Option	Genotype	Possible Offspring Colours
Brindle & White	1	Ay Ay kbr kbr si sw	- can only produce BRINDLE
			SOLID, BRINDLE & WHITE
			and/or all WHITE puppies no
			matter what the colour of the
			mate is.
	2	Ay Ay kbr ky si sw	- can produce BRINDLE
			SOLID, RED SOLID, BRINDLE
			& WHITE, RED & WHITE or all
			WHITE puppies depending on
			the colour of the mate.
	3	Ay at kbr kbr si sw	- can produce BRINDLE
			SOLID, BLACK BRINDLE
			SOLID, BRINDLE & WHITE,
			BLACK BRINDLE & WHITE
			and all WHITE puppies
			depending on the colour of the
			mate.
	4	Ay at kbr ky si sw	- can produce all colour options
			– BRINDLE SOLID, BRINDLE
			& WHITE, RED SOLID, RED &
			WHITE, BLACK BRINDLE
			SOLID, BLACK BRINDLE & WHITE, BLACK & TAN SOLID, TRICOLOUR and all WHITE puppies depending on the
			colour of the mate.

BLACK BRINDLE BULL TERRIERS

Phenotype	Option	Genotype	Possible Offspring Colours
Black Brindle Solid	1	at at kbr kbr si si	- can produce BRINDLE SOLID, BLACK BRINDLE SOLID, BRINDLE & WHITE and BLACK BRINDLE & WHITE puppies depending on the colour of the mate.
	2	at at kbr ky si si	- can produce all colour options except all WHITE – i.e. BRINDLE SOLID, BRINDLE & WHITE, RED SOLID, RED & WHITE, BLACK BRINDLE SOLID, BLACK BRINDLE & WHITE, BLACK & TAN SOLID and TRICOLOUR puppies depending on the colour of the mate.

Phenotype	Option	Genotype	Possible Offspring Colours
Black Brindle & White	1	at at kbr kbr si sw	- can produce BRINDLE SOLID, BLACK BRINDLE SOLID, BRINDLE & WHITE, BLACK BRINDLE & WHITE and all WHITE puppies depending on the colour of the mate.
	2	at at kbr ky si sw	- can produce all colour options – BRINDLE SOLID, BRINDLE & WHITE, RED SOLID, RED & WHITE, BLACK BRINDLE SOLID, BLACK BRINDLE & WHITE, BLACK & TAN SOLID, TRICOLOUR and all WHITE puppies depending on the colour of the mate.

It would very useful for the Bull Terrier breeder to know what colours could be expected from the matings of different coloured parents. To do this, the breeder needs to know the genotypes of their breeding dogs and bitches. Remember - a particular phenotype may result from a number of different genotypes. For example, a Brindle & White Bull Terrier may have one of four different genotypes. While this phenotype is easily observable, its genotype is not so clear. If the parents of the dog are known, then it is possible to be able to identify which genotype is resulting in its Brindle & White phenotype. Thus genotype can be inferred by considering the colours of an individual’s parents or from the colours of puppies already produced by that individual. If the genotype of both parents of a litter is known, proportions of different colours for that litter can easily be calculated mathematically. (Tables of these colour proportions have been prepared in the article “Colour in Bull Terriers – Part 2 – Inheritance of Colour – Full Version”). It is important to note, that these ratios apply to large numbers of individuals and will not occur in small litters but they still give an indication of probability. To use a human example: while a mother may expect a 50% chance of a boy or a girl, she may in fact produce four sons in succession and the fact that she already has four sons does not change the probability that she could have another. She could still expect a 50% chance of another boy. As the number of puppies in a litter is tiny in statistical terms, the actual proportions of the different colours cannot be expected. However, these calculations do show which colours are not possible in particular matings. In this article “Colour in Bull Terriers – Part 2 – Inheritance of Colour – Short Version”, a summarised version of colour breeding tables follow. These tables show possible colours resulting from matings but do not attempt to show either proportions within litters or the likely occurrence of these litter colour combinations (some colour combinations are much more likely to occur than others). For this more detailed information please consult the article “Colour in Bull Terriers – Part 2 – Inheritance of Colour – Full Version”. To use the tables, find the colour of the sire by looking across the top row to find the column heading corresponding to the colour, look down the left-hand column to find the row of the colour of the dam. The intersection cell of the column and the row show the colours possible.
GENERAL RULES OF COLOUR INHERITANCE IN BULL TERRIERS:

Two White parents always produce all White puppies. These White puppies may have coloured marks on their heads but they will always be almost all White in colour. Two White parents cannot produce a predominantly Coloured puppy.

A White parent can never produce a Solid Coloured puppy – it can only produce a Coloured & White or an all White puppy.

A Solid Coloured parent will never produce an all White puppy. Even with a White mate, a Solid Coloured parent will produce Coloured & White puppies but never all White.

Two Solid Coloured parents will produce all Solid Coloured puppies.

A Solid Coloured parent and a White mate will produce all Coloured & White puppies.

A Solid Coloured parent and a Coloured & White mate will produce half Solid Coloured and half Coloured & White puppies.

A Coloured & White and an all White parent will produce half all White puppies and half Coloured & White puppies.

In fact any Coloured & White parent will produce half Coloured & White puppies no matter what colour the mate is.

Two Coloured & White parents will produce a quarter Solid Coloured and a quarter all White puppies with half Coloured & White.

Brindle puppies will only result when either one of the parents is Brindle or White carrying Brindle. If a dog has a Brindle gene, they will show Brindle (either Brindle, Brindle & White, Black Brindle or Black Brindle & White) and only then can they pass Brindle on to their offspring. The only exception to this is if it is a White dog carrying that Brindle without any coloured marks to show it.

Two non-Brindle parents can never produce a Brindle puppy.

If Black & Tan, Tricolour, Black Brindle or Black Brindle & White dogs are bred with each other, the offspring will only be one of these four options.

It must be highlighted again that the actual proportions of the different colours presented in the tables will only be evident with very large numbers of puppies as a single litter of puppies is too small statistically to reflect this. The tables can however show possible colours that can result from a mating. In conclusion, coat colours in Bull Terriers are comparatively simple to understand as only four genes determine colour variation in our breed. Breeders can use the phenotype of an individual and the colours of the parents and grandparents to determine its genotype. Litters produced can confirm this genotype. Once the genotype is known, future possible litter colours can be predicted from these tables. By Tracey Butchart Illustrations by Duncan Butchart June 2009

REFERENCES

Barsh, G. 2007. How The Dog Got Its Spots. Nature Genetics: 39(11):1304-1306. Bowling, S. A. Color Genetics in Animals. http://bowlingsite.mcf.com/Genetics/Genetics.html Briggs, L. C. and Kaliss, N. 1942. Coat Color Inheritance in Bull Terriers. Journal of Heredity: 33: 223–228. Burford, A. G. The Genetics of Breed Color in the American Pit Bull Terrier. American Dog Breeders Assoc.Publication. Candille, S.I., Kaelin, C.B., Cattanach, B.M., Yu, Bin, Thompson, D.A., Nix, M.A., Kerns, J.A., Schmutz, S.M., Millhauser, G.L., and Barsh, G.S. 2007. Aβ-Defensin Mutation Causes Black Coat Color in Domestic Dogs. Science: 318(5855): 1418–1423. Coppinger, R. and Coppinger, L. 2001. Dogs – A New Understanding of Canine Origin, Behaviour and Evolution. Scribner, N.Y. Eberhard, E. 1971. The New Complete Bull Terrier. Howell Book House, New York. Glyn, R. H. 1950. Bull Terriers and How to Breed Them. Hall Publisher, Oxford. Harris, D. O. 1990. Full Circle – A History of the Colored Bull Terrier. D. O. Harris, USA. Hogarth, T.W. 1932. The Coloured and Colour Breeding. Walker, Galashiels. Hogarth, T.W. 1936. The Bull Terrier Notebook. Walker, Galashiels. Kerns, J.A., Cargill, E. J., Clark, L. A., Candille, S. I., Berryere, T. G., Olivier, M., Lust, G., Todhunter, R. J., Schmutz, S. M., Murphy, K. E. and Barsh, G. S. 2007. Linkage and Segregation Analysis of Black and Brindle Coat Color in Domestic Dogs. Journal of Genetics: 176: 1679-1689. Little, C.C. 1957. The Inheritance of Coat Color in Dogs. Comstock, Ithaca, N.Y. Mackay-Smith, W. E. 1980. From James to Jim: The Next Ten Years, 1969-1978. KNA Press. Ostrander, E. A. and Wayne, R.K. 2005. The Canine Genome. Genome Research: 15: 1706-1716. Schmutz, S. M. and Berryere, T.G. 2007. Genes affecting coat colour and pattern in domestic dogs: a review. Animal Genetics: 38(6): 539-549. Schmutz, S.M., Berryere, T. G., Ellinwood, N. M., Kerns, J. A. and Barsh, G. S. 2003. MC1R Studies in Dogs with Melanistic Mask or Brindle Patterns. Journal of Heredity: 94(1): 69–73.

Inheritance Of Colour

Living With Your Bull Terrier

Having fun with your Bull Terrier

Breeding your Bull Terrier