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The G locus: progressive graying in dogs

There are some breeds of dogs that have black or brown parts in their fur gray or fade early in the dog’s life. But so far it is unclear why Yorkshire Terriers, Bobtails and others Color fade get gray fur so early.

Want to learn more about dog coat colors?

Here you can find all the basics of the Genetic and Inheritance the coat colors. The article on pigment types explains the terms Eumelanin und Phaeomelanin. And this way is the complete one Overview of all fur drawings and colors.

Dog breeds with progressive graying

There are many breeds of dogs in which progressive graying occurs. Not surprisingly, many of them are loosely related to one another. What is immediately noticeable is that progressive graying appears to only affect dogs with furnishings (facial hair):

  • Bobtail
  • Bearded Collie
  • Tibet Terrier
  • Polish Lowland Sheepdog (PON)
  • Bedlington Terrier
  • Dandie Dinmont Terrier
  • Basset Griffon Vendeen
  • Bottle
  • Irish Wolfhound
  • Deerhound
  • Cesky Terrier
  • Kerry Blue Terrier
  • Havanese
  • Glen of Imaal Terrier
  • Lagotto Romagnolo
  • Spanish Water Dog
  • Bolonka Zwetna
  • Shih Tzu
  • Lhasa Apso
  • Yorkshire Terrier
  • Australian Silky Terrier
  • Pumi

The G locus

Everyone knows the gray color of the Bobtail, Bearded Collie or Yorkshire Terrier, but the gene responsible for progressive graying has not yet been found and cannot be tested.

But since one can safely assume a genetic cause, the hypothetical gene locus is named as Graying-Lokus or short G-Lokus.

Without being able to know more precisely, one currently assumes two alleles:

G – Progressive Ergrauung
g – No graying

In addition, one assumes that G behaves incompletely dominant:

G-Lokus Phenotype
G / G Heredity for the dominant allele leads to progressive graying.
G / g Mixed-breed animals are also said to be affected by progressive graying, but not quite as badly.
g / g No graying

Update 01/2020:

A study was published in 2020 according to which the previously separate intensity locus and the G locus could be the same mechanism.

The scientists were able to show that dogs with an intense coat color have several copies of a small gene segment in the KITLG gene than less intensely colored dogs.

This affected both phaeomelanin and eumelanin in the dogs examined. In the case of both pigment types, a decrease in pigment deposition with progressive hair growth led to a less intense color impression.

And since dogs with progressive graying actually wear furnishings, i.e. have steadily growing hair without a change of coat, this, in combination with the discovered genotype, could explain the progressive progress of the fading.

Especially with the poodle you will find all gradations and corresponding color names. Brown can be lightened to beige or “cafe au lait”, but is not wanted by the breed standard of the FCI. And black turns into blue (not to be confused with dilute) or silver-gray.

The dilution colors blue or lilac can theoretically also appear with progressive graying. But then the effect shouldn’t be so obvious, I think.

Gradations of progressive graying: from left to right gg – Gg – GG

Progressive Ergrauung

In the progressive graying will the black and brown Areas faded with time. Phaeomelanin is not affected in all dogs, but seems to fade easily in many as well.

In dogs with graying, lighter and darker shades of fur may show up, but the graying progresses fairly evenly overall.

Shear seems to accelerate the effect. Even if the hair initially appears darker, it grows a little lighter with each pass than before.

Basically, progressive graying behaves a bit like the horse’s mold:

The affected dogs will be born with dark fur and then clear up all over the body with increasing age, including the ceiling, flanks, legs and tail.

In Yorkshire Terriers, a saddle mark is formed from the black-and-tan at birth:

The graying can lead to a lightening of black to silver gray or from brown to red-gray to lead.

Which dogs have color fading?

Progressive graying only affects dogs with long hair, wire hair or curls!

Dark Face Masks (Em) do not appear to be affected by progressive graying and remain visible in adult fur. A prominent example of this are Kerry Blue Terriers.

Not every gray dog ​​is progressively gray

Progressive graying should not be confused with normal “turning gray around the muzzle”.

Even young dogs can turn gray at an early age and show the typical progress as with older animals. Here the graying begins slowly from the muzzle and forms a light face mask, but rarely progresses over the whole body.

Gray snouts in senior dogs

Dogs too Roan, Domino, Merle oder Dilute can look very silver-gray in adult fur and can easily be mistaken for a progressively graying dog.

Dogs with strongly lightened phaeomelanin in sable or agouti also look gray-spiked, e.g. schnauzers in pepper-and-salt or wolf tip.

However, these dogs are all born with lightened areas of the coat, whereas dogs with progressive graying are born as normal, dark-colored puppies.

Theoretically it is possible that a dog expresses one of these factors at the same time as the progressive graying, but the combinations seem almost never to occur in practice or are then not quite as obvious in the phenotype.

No progressive gray! From left to right: Light Phaeomelanin, Domino, Merle, Dilute

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[1] http://www.doggenetics.co.uk/greying.html

[2] Kalie Weich,Verena Affolter,Daniel York,Robert Rebhun,Robert Grahn,Angelica Kallenberg, Danika Bannasch; Pigment Intensity in Dogs is Associated with a Copy Number Variant Upstream of KITLG; Genes 2020, 11(1), 75; https://doi.org/10.3390/genes11010075


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