Yarraman Australian Cattle Dogs


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Colour

General Information about coat colour in the ACD

There has been more selection for variation in the dog than almost any other domestic animal. These differences include size, body shape, coat type (smooth, rough, long, short) and colour. The type of coat a dog has is usually associated with the work they were originally bred to do, though some have been altered over the years for a more 'flashy' look in the world of dog showing. The colour of the coat has, in many cases, evolved due to the work the dog was intended for, usually to either be, or not be, easily seen against the working background.

In the Australian Cattle Dog the two accepted coat colours are 'red', properly known as 'sable', and 'blue', properly known as 'black and tan' or 'tanpoint'. There are other colour variations that appear from time to time but these two are the ones breeders would hope for in litters.

When you look at an ACD and see 'red' or 'blue and tan' this is the PHENOTYPE - what is on display. What you don't see but controls the colour of the dog is the GENOTYPE.

Every dog has two alleles for each gene that controls coat colour and a puppy inherits one copy of each these alleles from its sire and one copy from its dam.

In the 'genetic colour chart' for a dog only the first shown allele in each series is expressed, this is the dominant allele. The other is carried. For example, a black dog may be B/B or B/b (when not known whether the carried allele is B or b it is shown as B_). If the dog is homozygous for B (B/B) then it cannot produce brown coloured offspring even if mated to a brown dog because both of its alleles are for black, and the black alleles, being dominant, will over-ride the brown making all the puppies black. However if it is heterozygous B/b then it carries the allele for brown, and mated to another heterozygous B/b there is a 25% chance of brown puppies in a litter (over a large sample) when the b/b combination comes together.

Dominant and recessive, homozygous and heterozygous

In Australian Cattle Dogs sable is dominant to tanpoint (i.e. red is dominant to blue), so a red ACD can carry blue and if mated to a dog that is blue or a red carrying blue can produce blue puppies, but a blue ACD cannot carry the more dominant red allele, so two blues mated together cannot produce red pups except with the assistance of another allele (e), which does happen but is uncommon. In 99.9% of cases a blue to blue mating will produce blue puppies

Homozygous means the allele pairing is the same, for example, B/B (only has the alleles for black). Heterozygous means that the allele pairing is different, for example B/b (is black and carries brown).

GENE SERIES

A (agouti) - is a protein that affects the amount of melanin in a growing hair and causes a banding effect. It is a term taken from the name of a South American rodent with this type of colouring, but a more commonly understood example would be that of a wild rabbit. The agouti gene has been mapped to dog chromosome 24. No breed of dog has all of the alleles and it is impossible to state with absolute certainty what the order of dominance is, however ongoing work into coat colour seem to suggest that it is likely (in order of decreasing dominance):

a^y (sable)
a^w (wild)
a^s (saddle)
a^t (tanpoint)
a (recessive black)

Those alleles that come into play in the ACD are shown below - those that do not directly affect the ACD are not shown here.

a^y (sable) - this is also sometimes described as dominant yellow. Sable gives a red/yellow phenotype (appearance), but the hair tips are black (caused by eumelanin). The extent of black tipping can vary considerably from light sables (where the amount of tipping is minimal and may disappear entirely in the adult coat) to darker sables (where there is a greater degree of tipping and this may remain in the ACD's coat throughout it's life - these 'smutty reds' are considered undesirable in the show-ring). More black tipping than on average is believedby some to be associated with a dog having the heterozyous (a^y/a^t) genotype. Sable is the common genotype of red Australian Cattle Dogs either in a homozygous or heterozygous form.

a^s (saddle tan) - Eumelanin is restricted to the back and side regions like a saddle (this pattern is the one seen in Airedales and German Shepherds) This is undesirable in the ACD. The puppy will look like a tanpoint as a puppy but as the dog matures the amount of black 'creeps' back exposing the tan below.

There is a school of thought that a^s is a^t with modifiers which cause a reduction in the amount of eumelanin as the dog develops. Some ACD puppies will show early signs of creeping on the backs of their ears, which will be red tinged. Some will only ever display minimal creeping (tan further up the legs than normally found in a tanpoint and black eye patches may decrease leaving a tan eye patch in its place), whilst others will become predominantly tan with only a small saddle of black on their backs. CLICK HERE

a^t (tanpoint) - This a dog that is coloured, more often black or brown, on the dorsal area with tan points above the eyes and on the muzzle, cheeks, chest, throat, stomach, lower legs and under the tail. The points can range from creamy to mahogany in colour. This colouration is found in many breeds, for example the Dobermann and Rottweiler. This is the typical colour variety described in Australian Cattle Dogs as blue and tan, or tanpoint. Since red ACDs have an allele further up the chain of dominance blue ACDs are homozygous a^t/a^t. However, as shown below two blues may produce red puppies from time to time.

E (extension) - This is the Melanocyte Stimulating Hormone Receptor Gene (MSHr) or Melanocortin Receptor 1 gene (MC1R), a gene that has been mapped to dog chromosome 5. This gene has three alleles, the most common being E and e. These alleles control the extension of eumelanin over the dog's body. The dominant form, E, is normal extension and the dog will have some black or brown in its coat because of the production of eumelanin. The recessive form, e, is non-extension. When a dog is homozygous for non-extension (e/e), its coat will be entirely red/yellow (phaeomelanin based). The third allele at E is EM - known as melanistic mask. This allele allows agouti to bind some of the time and so fawn pigment will be made on the body, however the melanocyte stimulating hormone binds to the face. This means any fawn/red coloured dog must be so because of an agouti genotype and are never non-extension e/e (see below) as they require an EM allele to produce the black mask. Occasionally red Australian cattle dogs will have 'blue' muzzles, and even very occasionally black markings around the eyes, it is possible that this is caused by this third allele, but if so, it is rare. The vast majority of ACDs are homozygous E/E

The non-extension (e/e) dog does not have any black/brown hair in its coat and this helps differentiate it from an Agouti red. e/e ACDs have likely been cropping up in litters since the beginnings of the breed. When one parent is red then they will not cause any comment as red puppies would be expected in the litter. However, when both parents are blue then this is a sure indicator that both parents carry the recessive e and the puppy is homozygous e/e. The first DNA tested e/e reds were bred by Suzanne Nevada of Silveraurora ACDs. You can see photos and read about one of them here http://www.telusplanet.net/public/ranchrat/hyblade.html and pedigree can be seen here
http://www.acdpedigree.com/cgi-bin/geneal.cgi?op=tree&index=38963&gens=5

Recessive genes can be carried for many generations before the right (or some would say wrong) combination comes along for the recessive to be expressed, if it is a particularly rare recessive then it could be carried for many, many generations.

B (brown) -the dominant form of this two allele gene series is B which programmes the colour and pigment of the ACD to be black. In the homozygous recessive form (b/b) the pigment (nose, lips and eyerims) and colour of the dog will be brown, there are now 3 common mutations recognised - b^s, b^d and b^c - and perhaps more rare ones that lead to brown instead of black eumelanin production. Whilst b/b has no effect on the A-series, it is possible to have an ACD that is e/e and also b/b, so the dog will be red/yellow with brown pigment. b/b dogs also have lighter (could be described as 'toffee coloured') irises. Brown, sometimes described as chocolate, ACDs are rare but not unknown.

D (dilution) - ACDs are believed only have the dominant form of this 2 allele gene series, which is D and d. D/D produces undiluted black or red/yellow. Dogs that are d/d may be blue/charcoal gray as a dilution of black or pale brown as a dilution of brown and so on.

C (albino) - The typical gene associated in other species with Tyrosinase. Controls the intensity of melanin in the coat. The dominant form C is described as 'full colour'.

Sponenberg and Rothschild describe a gene they named I for Intense that dilutes only phaeomelanin (red/yellow). Dogs with diluted phaeomelanin may be described as apricot, buff, cream or lemon. It is likely such a gene exists but has yet to be identified in the dog.

S (spotting) - The first gene responsible for at least some of the spotting patterns has been identified and published in 2007. Potential mutations causing some forms of spotting have been identified. This gene is called MITF.

The alleles currently at this series that affect the ACD are (in decreasing dominance):-

s^p (Piebald) - In a piebald dog the spots appear randomly anywhere on the body, they are not consistent in size or location, the white often crosses the back, which differentiates piebald from another allele known as Irish Spotting. Piebald is often combined with large markings on the body, sometimes described as 'slabbing' or 'plating'. A piebald dog often has colour and white in an approximately 50/50 ratio. ACDs witha large amount of body spots are displaying the effects of the piebald allele.

s^w (Extreme White Spotted) - A dog that is homozygous for s^w/s^w will be mainly white, for example, a Sealyham terrier. ACDs with no coloured markings, or markings confined to the head and, possibly a tailspot, when born are most likely homozygous at this allele.

The line drawn between a dog with few piebald spots and a dog that is extreme white spotted is not that clear-cut.

Australian Cattle Dogs can be homozygous piebald (s^p/s^p), homozygous extreme white spotted (s^w/s^w) or heterozygous (s^p/s^w) combined with the ticking gene.

T (ticking) - This is a two allele gene series where the incompletely dominant mutation T can only be expressed in areas that are white due to the White Spotting series (S). The colour of the ticking is the colour the dog would be if the white spotting gene had not been present (in the case of ACDs that would be black and tan or red). Dogs that are t/t will not be ticked. Ticking is not visible at birth, it develops over a period of time, hence the reason that ACD pups are predominantly white when born.

M (merle) - ACDs are never merle but are often described as such, particularly in those that are mottled. So at this locus ACDs are m/m

K^B (dominant black) - It was long believed that solid coloured dogs were at the top of the dominance chain for the A series and was known as A^s. However, Kerns et al. (2003, 2005) recently showed, through DNA studies, that this 'Solid' allele is not an agouti allele. They, instead, describe dominant black as a genotype that is epistatic to fawn, sable etc. and occurs at another locus which is now known as K^B (for blacK).

The order of dominance is shown to be:

K^B - dominant black
K^br - brindle
k^y - normal

Brindle ACDs are, to the best of my knowledge, unknown therefore the two in this series that should concern us are K^B and k^y. Dogs which have two recessive alleles (k^y/k^y) can express a variety of phenotypes. All black-and-tan dogs or dogs with tan points are k^y/k^y. All fawn or sable dogs are k^y/k^y whether they have a melanistic mask or not. Red dogs that have an e/e genotype however, could be any genotype at the K locus.

The Stanford group chose to name this allele k^y since it allows yellow or phaeomelanin pigment to show. Where it shows depends on the alleles at the agouti locus.

A simple chart

Most new ACD breeders start off just wanting to know if they will have red or blue puppies. So, I will show some Punnett squares below that may help work this out. The assumption is that all the dogs involved in these hypothetical breedings are E/E so there will be no red puppies in blue matings. It doesn't matter which dog is sire and which dog is dam.

These Punnett squares show what is possible, but genetics are like a coin toss in small samples (and a litter would be considered a small sample). So, in some of the matings where there is more than one possible outcome it may be that not all of them will be seen, or the percentages appear to be skewed. However, when a large number of offspring with parents of a known alelle combination are studied then the percentages expected are borne out as Mendel predicted in his theory.

Mating two blue ACDs together (a^t/a^t x a^t/a^t):-



Alleles
carried by
parents
a^t a^t
a^t a^t/a^t
(blue)
a^t/a^t
(blue)
a^t a^t/a^t
(blue)
a^t/a^t
(blue)

Both parents are a^t/a^t and can, therefore, only pass on a^t alleles to their offspring. All puppies will, therefore, be blue.

Mating a blue ACD with a homozygous red (a^t/a^t x a^y/a^y):-

Alleles
carried by
parents
a^y a^y
a^t a^y/a^t (red
carrying
blue)
a^y/a^t (red
carrying
blue)
a^t a^y/a^t (red
carrying
blue)
a^y/a^t (red
carrying
blue)

The red a^y allele over-rides the a^t allele, so all puppies will be red and will carry the allele for blue.

Mating a blue ACD with a heterozygous red (a^t/a^t x a^y/a^t):-

The heterozygous red carries the allele for blue.



Alleles
carried by
parent
a^y a^t
a^t a^y/a^t (red
carrying
blue)
a^t/a^t
(blue)
a^t a^y/a^t (red
carrying
blue)
a^t/a^t
(blue)

In such a mating you could expect, over a large sample, to have 50% red puppies carrying blue and 50% blue. So, from this mating both reds and blues are possible.

Mating a heterozygous red (carries blue) and a homozygous red (does not carry blue) (a^y/a^t x a^y/a^y):-

Alleles
carried by
parents
a^y a^t
a^y a^y/a^y
(red)
a^y/a^t (red
carrying
blue)
a^y a^y/a^y
(red)
a^y/a^t (red
carrying
blue)

Over a large sample 50% of the pups would be homozygous red a^y/a^y, not carrying blue and 50% would be heterozygous reds a^y/a^t, carrying blue

Mating 2 homozygous reds together (a^y/a^y x a^y/a^y):-

Alleles
carried by
parents
a^y/a^y a^y/a^y
a^y a^y/a^y a^y/a^y
a^y a^y/a^y a^y/a^y

The homozygous reds only have a^y alleles so can only pass them on, therefore, all puppies will be homozygous reds too.



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