THE BRINDLE GENE

Brindle is one of the recessive genes on the K locus. There are three K locus genes - K (dominant black), k^br (brindle) and k (non-solid black - allows A locus to be expressed). K is the top dominant and k is the bottom recessive. k^br sits between the two. It is entirely dominated by K (so just one K gene will stop brindle from being expressed), but is dominant over k, so a brindle dog can have the genotype k^brk^br or k^brk.

A dog with one or two k^br genes will express whichever genes it has on the A locus, but any and all phaeomelanin (red) in the coat will be brindled. This means that the extent of the brindling on the coat depends on the A locus. The following list shows how the different A locus genes affect the appearance of brindle.
Brindle + A^yA^y (sable) - dog will be solid brindle (possibly with darker areas on the back and head where the black tipping on the sable would be)
Brindle + a^ta^t (tan points) - dog will be black with brindle points
Brindle + a^sa^s (saddle-marked) - dog will be brindle with a black saddle
Brindle + a^wa^w (agouti/wolf grey) - effect on dog is unknown. Would most likely appear to have brindle points, or brindle may not appear at all
Brindle + aa (recessive black) - dog will be solid black (recessive black does not allow the production of phaeomelanin in the coat)

Brindle typically appears as black stripes on a red base. The stripes are eumelanin and the base is phaeomelanin, so the appearance of those pigments can be changed by any of the genes which usually affect them.
Eumelanin (the stripes) can be affected by: merle (and harlequin), liver, dilution, greying, recessive red
Phaeomelanin (the base) can be affected by: chinchilla (albino series)
And of course, white markings and ticking can occur on any brindle dog.

VARIATIONS IN STRIPING

Stripe width can vary greatly, and it is not known which genes, if any, are responsible for this variation.

The French Bulldog on the left shows very heavy striping and appears almost completely black. This is sometimes called "black brindle" or "reverse brindle". The Great Dane on the right has very light striping, with the coat predominantly red rather than black. The Dane photo was taken by Kenzie and the Bulldog by June.

This French Bulldog shows even heavier black striping than the one above. There is only a very small bit of tan visible on the hip, and the rest of the dog appears solid black. This photo was taken by Kenzie.

VARIATIONS IN BASE COLOUR

The base colour on a brindle can vary as much as red can usually vary, from a deep Irish Setter colour to a light cream. A light base coat on a brindle is generally due to the dog being c^chc^ch (chinchilla) on the C locus. Chinchilla dilutes phaeomelanin (red pigment) to cream, but has no effect on eumelanin (black pigment).

These are all details taken from photographs of brindles with black stripes.

BRINDLE WITH A MASK

A dog which has at least one E^m gene on its E locus will have a black mask. This is an area of eumelanin covering the muzzle and sometimes the ears. If a dog is a brindled sable (brindle gene + sable gene), it'll be brindle all over, and on dogs like this masks may be visible.

SILVER BRINDLE

Sometimes a brindle dog with black pigment may have silver stripes, usually on a cream background (never deep red). This colouration is generally associated with sighthounds, particularly Afghan Hounds. The overall effect may be similar to how a blue brindle (dd dilution gene) would look. Silver brindle is caused by the greying gene (G locus), which turns black to grey as the dog ages.
Sometimes dogs with black stripes and a very light cream base (see above) are also referred to as silver brindles.

The Afghan Hound on the left has completely grey stripes. The Akita Inu on the right has some black stripes and some grey - this is probably just due to the light base coat and is not necessarily caused by the greying gene. The Afghan photo was taken by Kenzie.

BRINDLE AND LONG FUR

Long and wirey fur can obscure brindle markings by making the stripes less distinct.

Even between longhaired breeds, the visibility of brindle can vary. The Skye Terrier here has very distinct stripes and is obviously a brindle, but the Afghan Hound just appears to be a muddy brown. The main way we can tell this Afghan is brindled is simply its muddy-coloured coat - this colour occurs almost exclusively on brindles and never on normal solid reds or sables. It also appears to have some lighter and darker areas, which also suggest it is a brindle.

This Borzoi's brindling is very obvious on the short fur on its head, but less obvious on the longer fur on its body. The large areas of black on its back suggest that it has black tipping (as some sables do). Black tipping on a sable brindle will never be brindled, just like any other area of black. This photo was taken by Kenzie.

These three dogs show brindling on wirey and curly coats. The Irish Wolfhound on the left has very obvious brindling on its head and legs, where its fur is shortest, but it gets more grey and blurry on its body, where its fur is longer and thicker. The Bouvier and Deerhound in the middle and on the right both have the greying gene, which makes their stripes turn grey. This makes it even harder to see the brindle stripes on their thick fur, because they blend into the base colour. The classic Deerhound colour is grey, but most are in fact brindle with the greying gene, like this dog.

BRINDLE TAN POINTS AND SADDLE MARKINGS

Because the brindle gene allows expression of the A locus, any A locus coat patterns can show brindling on their red sections. The main patterns are sable (A^yA^y), tan points (a^ta^t) and saddle markings (a^sa^s). A sable brindle will appear solid brindle (in fact, all solid brindles are sables). A tan pointed dog with the brindle gene will appear black with brindle points instead of tan, and a saddled dog will be brindle with solid black on its back and/or neck, tail and head.

This is my own mixed breed, Rosie. She has brindled paws and legs, which points to her being genetically tan pointed (a^ta^t). Her other tan markings aren't visible, but it is likely that her chest markings are obscured by the brindle and her long fur, and her face markings are obscured by a hidden black mask.

This little group of Plott Hounds clearly show some of the agouti locus patterns with brindle. The dog on the left of the first picture is a brindle with the saddle marking gene (a^sa^s). The second picture shows this dog more clearly, and you can easily see the solid black on its back and tail. The other two dogs in the first picture have brindled tan points, like Rosie above (but their markings are more visible because they're shorthaired). Pictures taken by Kenzie.

BRINDLE MERLES

These are dealt with on the merle page.

LIVER AND DILUTE BRINDLES

A brindle dog will have liver (brown) stripes if it is bb on the B locus, blue stripes if it is dd on the D locus, and isabella stripes if it is both dd and bb. Dilution affects phaeomelanin (red) too to some extent, so the base colour will be relatively light (certainly not a deep red colour, but more likely cream).

From a distance this Neapolitan Mastiff looks completely blue, but close up you can see a few light tan-coloured stripes. There are so few stripes visible because this is a "black brindle", i.e. a brindle with very heavy dark stripes which obscure most of the red underneath. A blue brindle will be more obvious when the stripes are lighter.

This dog doesn't look like it, but it is actually an isabella brindle! Its genotype is bbdd (liver dilute) The dark stripes have been diluted to such a light shade of brown that they blend in with the light red base coat and have become very difficult (nigh on impossible) to see.

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