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The Truth Behind "Silver" Labradors

 

 

People that breed silver labs register them as chocolate. A dog's genetic makeup is very complex (like us) and many
genes are involved in coat color. The genes are all present in every dog however only certain ones get "turned on" like
a switch and all others are off depending on what breed or what goes into a puppy in the case of a mixed breed. A Labrador's
coat color is dependent on many genes being turned on and off - the ones we commonly think of that dictate color in our
breed are the B and E genes of coat color being "turned on" - other genes like T for ticking is always turned off and still other
genes like the A gene causes a dog's coat to be all one color. We know that If a lab has BB or Bb then black is dominant,
if it has bb then the dog is chocolate. However the E gene acts as a epistemic gene or "masking" gene; in other words if the
dog has Ee or EE then the color is solely dependent on what is present at the B gene (BB, Bb, or bb) but if the dog has ee
then it will ALWAYS be yellow no matter what is present at the B gene.

The silver coloration comes into play when the D gene is turned on - which does not normally happen in labradors. If the
D gene is dd then it will "dilute" the coloration if the B gene is bb in labradors. In other breeds the dilute combo (dd) can
make a Bb or BB dog gray or "blue". A dog like the Doberman has this dilute gene pattern and therefore "blue" dobies
can arise from a black Doberman that has this dilute combination. Other breeds like Great Danes, Chow Chows, and
German Shepherds can be diluted. Some breeds accept the color and others do not.

The breeders of silver labs say that it is the B gene working in conjunction with the C gene - (C for "concentration" that
can cause fox reds in our breed when combined with ee and it can influence the concentration of black or chocolate
expression as well - This is why some chocolates are darker than others, and the colors range from very dark chocolate
to a very light silvertone ). In either case, the genetics show that the dogs are actually chocolates, and is registered as such,
independent of actual visual color. Coat Color Inheritance


Color In The Labrador Retriever

Key:
EEBB =Basic Black (BB)
EEBb =Black that carries Choc. (Bc)
EeBB =Black that carries Yellow By)
EeBb =Black that carries Yellow and chocolate (Byc)
eeBB =Yellow (Yy) [does not carry chocolate]
eeBb =Yellow that carries Chocolate (Yc)
eebb =chocolate pigmented yellow ~ No Black Pigment (NBP)
EEbb =Chocolate (CC) [does not carry yellow]
Eebb =Chocolate that carries yellow (Cy)

Diluted or Pale Colors

last updated on March 10, 2007 by Proff. Sheila Schmutz

 

  • "Dilution" Loci

    This webpage is part of a series on Dog Coat Color Genetics and was last updated on March 10, 2007 by Sheila Schmutz

     

     

     

    Dilution of Eumelanin and/or Phaeomelanin

    Blue

    Blue or charcoal grey, as a dilution of black, has recently been shown to be caused by the melanophilin gene (MLPH). The blue caused by this gene could be termed "born blue" since it is present from birth. The Blue Doberman is a dog that has the black on its upper torso diluted to slate grey and its tan undersides diluted to a paler shade of tan. The dilution of the tan is much less noticeable than the dilution of black, both both eumelanin and phaeomelanin are affected in dogs of "d/d" genotype.

  • Philipp U, Hamann H, Mecklenburg L, Nishino S, Mignot E, Schmutz SM, Leeb T. 2005. Polymorphisms within the canine MLPH gene are associated with dilute coat color in dogs . BMC Genetics 6:34-. (This article is published in a publicly accessible online journal at http://www.biomedcentral.com/1471-2156/6/34)
    Blue is the name of a coat color used in breeds like the Great Dane to specify a eumelanin pigmented dog that is diluted to a blue grey. The litter at the left shows blue and black pups in the same litter.

    Blue is also used to describe a coat color in the Chow, as shown by Shadow on the right, and in the Shar-Pei. It also occurs occasionally in Newfoundlands, Large Munsterlanders, Australian Shepherds, Doberman Pinschers, and other breeds. Hence it occurs in a wide variety of breeds and may be quite ancient in origin.

  •  

    Brown

    Some authors refer to brown as a dilute color. Somehow this bothers me. I don't think of brown as diluted black, which to me is gray or in dog terms "blue". Brown is created by a modification of eumelanin so in some sense I suppose I can understand why it is sometimes lumped with the diluter gene effects.

    The gene for brown is TYRP1 and the 3 mutations causing brown are now known but this is discussed on another page about brown in this series.

     


     

    "Dilution" Loci

    Locus Symbol Gene Action Proven in Species Dog Chromosome
    D for dilute (Little) MLPH eumelanin diluted to grey or blue & phaeomelanin paled mouse, dog 25
    C for color (Little) tyrosinase (TYR) albinism, dilutes phaeomelanin & eumelanin mouse, cattle, human (not dog) 21
    P for pink-eyed (Little) P gene pink eyes & "white" coat mouse 5
    G for greying (Little) ??? progressive greying poodles and horse ?
    I for Intense (Sponenberg) ??? only phaeomelanin diluted ? -
    ? MATP phaeomelanin diluted as co-dominant, eumelanin as recessive horse (palamino & buckskin, cremello & perlino) 4
    Slaty TYRP2 eumelanin co-dominant dilution mouse 22

    last updated on March 10, 2007 by Proff. Sheila Schmutz

    This webpage is part of a series on Dog Coat Color Genetics and was last updated on July 1, 2006 by Sheila Schmutz

  • Black versus Red
  • Brown
  • DNA Diagnostic Services
  •  

     

    The Genetics of

    Silver Labs(GRAY)

              The silver coat color in Labradors has gained much attention recently and is a very controversial topic
     (see The Labrador Coat Color Controversy: Do Silver Labs Really Exist?). Reasons for the controversy stem from the
     lack of information available to trace the origins of this color in the breed as well as the fact that the AKC standard for
    the Labrador breed does not acknowledge silver as an acceptable color for a Lab. Some breed enthusiasts consider
    the silver coloration to be a sign of impurity of the bloodline, however, what geneticists have come to understand of
    recessive alleles is that they may be passed through many generations going undetected, such as the allele for tan
    points discussed above.

        The range observed in silver coloration suggests that silver occurs through a modifying gene. There have been
    several possible outcomes observed for the silver Lab:

    NEW TEST FOR THE DILUTION GENE

    Black Lab + silver modifier = charcoal gray coat with a "sparkly"-like appearance. Nose: dark gray; Eyes: dark to light gray

    Chocolate Lab + silver modifier = "mousy"-brown gray coat. Nose: same as coat; Eyes: yellow to gray-yellow

    Yellow Lab + silver modifier = platinum to pale silver (yellow with gray casting). Ears: gray (instead of red-toned);
                                                   Nose: dark to pale gray; Eyes: dark to pale gray.

              There are several possible explanations for the silver coat color in Labs. The first explanation would attribute this
    rare color in the breed to the D locus. Recall that the alleles of the D locus modify the color determined by the B locus.
    Therefore, if a dog is homozygous or heterozygous for black at the B locus, presence of homozygous recessive "d"
    at the D locus would dilute the black pigment to appear blue. Alternatively, if a dog is homozygous for chocolate at the
    B locus, presence of homozygous recessive "d" at the D locus would dilute the chocolate pigment to appear silver.
    The absence of the corresponding "blue" phenotype in the breed, however, would seem to argue against this explanation.

              Another explanation for silver coat color in Labs would attribute this color to the C locus. There is an allele mutant
    at the C locus that has been determined to cause silver coat color and blue eyes in dogs. The "cb" allele is believed to
    be a type of albinism. Since alleles at the C locus influence red pigment only, effects of the "cb" allele should only be
    observed in dogs homozygous "e" at the E locus. Therefore, a silver Lab would not only have to receive the yellow
    allele from both parents, but also receive the silver allele from both parents (which is recessive to the common "cch" allele).   
    This allele would explain the silver-toned modification of coat observed in yellow Labs in the presence of the recessive
    "e" allele, however it would not explain the eumelanin modification in the black or chocolate-based silvers (since the C
    locus alleles primarily dilute phaeomelanin).

          Likewise, the possibility of a "partial loss of function" mutation that may have occurred in the dominant "E" allele resulting
    in  muted tones of eumelanin would not explain the modification of phaeomelanin (yellow).

    An alternative explanation for explaining the modification of both eumelanin and phaeomelanin again returns to the
    wild-type/gain-of-function "E+" allele that encodes for a normal functioning Mc1 receptor. If this allele either occurred as
    a spontaneous mutation or was introduced into the breed through interbreeding, this might explain the modification
    occurring in all three colors, particularly when one considers the following:

    When one traces the pedigrees of some silver Labs, one finds a history of other color oddities occurring in some related
    bloodlines to the silver Labs. Occurrences of "black-casting" in chocolates, muted chocolate coloration ("card-board box"
    coloring), as well as the occasional occurrence of black puppies being whelped from two chocolate parents suggests that
    these "chocolates" were probably not chocolate at all but rather E+ yellows. As such, it is conceivable that the Agouti alleles
    could produce an intense red pigment resulting in deep red (interpreted as chocolate especially in the absence of "saddling"
    modifiers) or diluted, muted red (card board box color) due to further modification by the alleles of the C locus). In black Labs,
    an ayayEE+ genotype could produce a muted black color (because of the presence of both receptor types) especially if
    the alleles at the C locus were cch, thus resulting in a deep charcoal, silvery coat appearance. This suggests a possible role
    of E+ for the silver coloration as well as for a multitude of other coat color variants that occasionally occur in the breed.

    AND WHAT IS A SILVER Labrador? 

    As written in the Book By Show Judge Breeder Richard Edwards in England, Titled
    The show Labrador retriever in Great Britain and Northern Ireland 1945-1995

    Tells of the cross breeding to the Labrador to improve coat, lines and set

    Outcrosses were made to:.

    Labrador and Flatcoat
    Labrador and Pointer
    Labrador and Whippet/Greyhound
    Labrador and Sheepdog
    Labrador and Foxhound
    Labrador and Elkhound
    Labrador and Chow

     



    Breeding the Labradors, most of my Husbands life who was born 1931, I have seen and owned a lot of
    Labradors you could see some of the traits of the above Crosses.  Even now at age 75 we find it is not
    so surprising to see the Gene pool of the Show and Field Labrador still producing Labradors that do look like they
    are cross-bred. The Book Calls them the Barn yard look, and to the Labrador Fancy  who say their Labrador
    is pure, we ask Pure What?????

    (ANSWER) 

    PURE American Labrador Retriever.  Who will never be just one look,  this makes the breeding such a
    well argued  "mine is better than yours. "   Now Add the odd colors that show up, The latest  are
    SILVER/ "SPARKLY"-GREY  birthing from the chocolates and the SLATE/GREY from the Black's
    Where in the above crosses, added the gene?????  We ask.  Or is it a mutation being studied by
    Dr Mark Neff at Berkley in Calif.

    MUTATION HAS NOW BEEN FOUND IN CANADA, PROFESSOR SCHMUTZ

    Test for Gene Dd can be done at Health Gene Molecular Diagnostic and Research Center Toronto Canada

    last updated on March 10, 2007 by Proff. Sheila Schmutz DILUTE GENE FOUND, YOUR LAB CAN NOW BE TESTED.

    Below is an example of the type of DNA markers being studied at Berkley by Dr. Neff.

     

     

    Black versus Red

    Black, or black and white is a very common coat color in many dog breeds. Red is the classic color associated with the Irish Setter. However red also occurs in many other dog breeds in paler shades ranging through red to orange and yellow. It would appear that most of the hunting dogs that have black variants, such as German Shorthairs, German Wirehairs, and Pudelpointers are black because they have an E alllele at the MC1r gene. The Large Munsterlander is "always" E/E and black. However the Amreican Brittany and the Irish Setter are always e/e and red or orange or yellow. But the Small Munsterlander and German Longhair are brown, not red, and are also E/E due to the interaction of another gene B, explained below.
    The gene causing red/black is the Melanocyte Stimulating Hormone Receptor Gene (MSHr), also called the Melanocortin Receptor 1 gene (MC1R). This gene has two common alleles E and e. When E is present in a dog, it has some black or brown in its coat because of the production of eumelanin. This is the dominant allele in the series. Dogs that are e/e are red or yellow due to phaeomelanin production, and this is the recessive genotype.

    These 2 Dachshunds exemplify the two genotypes at this locus. The red dog has a black nose but is a clear red and has the genotype e/e at MC1R. The black is a black-and-tan and has an E allele, however his black-and-tan pattern is due an agouti allele (at)(see the agouti page for more details).

    There is a third allele at the E locus, E which is discussed on the page about Melanistic Mask. Melanistic masks do not occur in the hunting breeds.

    There are Dachshunds, such as the one shown, and dogs of other breeds that have red hairs with darker or black tips on them. These dogs do not have an e/e genotype. This non-solid red is caused by an allele at the agouti locus, ay. Other breeds such as Chows also fall into the category of not being red because of an e/e genotype. The colors tan or fawn, typically associated with agouti, are not always that easily distinguishable from the red of an Irish Setter. Depending on the breed, one red or the other is more common and in most breeds only one or the other red occurs.
    In some breeds, such as Labrador Retrievers the dogs are more yellow than red. The shade varies as is illustrated by the two littermates above whose parents were also both yellow.

    The MC1R gene has been mapped to dog chromosome 5.

    Little did not include the Hungarian Vizsla in his studies. They are hunting dogs which are typically gold to red and typically have brown noses because they are also homozygous for the recessive brown allele/s at the B locus. (see Brown for further details)
    This very white coat color is desirable in English Setters but it makes it difficult to tell what color the pigmented part of her coat is. By MC1r testing, she is e/e and therefore red.

    Breeds in which yellow-to-red dogs of the "e/e" genotype have been detected

    Note that in some breeds dogs with an e/e genotype are more often cream to white than yellow to red (see page on white for a discussion of these breeds).

  • Newton, J., A. Wilkie, L. He, S. Jordan, D. Metallinos, N. Holmes, I. Jackson and G. Barsh. 2000. Melanocortin 1 receptor variation in the domestic dog. Mamm. Genome 11:24-30.
  • Everts, RE, Rothuizen,J. and van Oost,B.A. 2000. Identification of a premature stop codon in the melanocyte-stimulating hormone receptor gene (MC1R) in Labrador and Golden retrievers with yellow coat colour. Anim. Genet. 31: 194-199.
  • Schmutz, S.M., J. S. Moker, T. G. Berryere, and K. M. Christison. 2001. A SNP is used to map MC1r on dog chromosome 5. Animal Genetics 32:43-44.
  • Thomas, R., M. Breen, P. Deloukas, N. G. Holmes and M. M. Binns. 2001. An integrated cytogenetic, radiation-hybrid and comparative map of dog Chromosome 5. Mamm. Genome 12:371-3100.

    Brown

    The two dogs at the left are representatives of the two possible color phases of the Large Munsterlander. Most Large Munsterlanders are black and white but occasionally a brown and white one is born. All Small Munsterlanders are brown and white.

    The reason that the German Longhair, who is E/E, is always brown or brown and white and the Large Munsterlander, who is also E/E is usually black and white, is due to another gene - B (for brown and black from Little's labelling) or Tyrosinase Related Protein 1. There are actually 3 common mutations and perhaps additional rare ones that occur in this gene which result in brown instead of black eumelanin production. The black allele B is dominant to the brown alleles (bS,S, bc). The nose leather, pads, and eye rims are also affected by this gene. They are black if a B allele is present but brown if not.

    In dogs which are yellow to red (e/e at MC1r), TYRP1 mutations affect the nose and pad coloration, changing it from black to brown. The yellow lab puppies, above, both have black noses but the Vizslas have brown or flesh colored noses.

    All dogs which have brown coat color have at least one E or Em allele so that eumelanin is produced. The German Longhair, at the left, is homozygous for one of the common mutations. Her genotype is bdbd. The Large Munsterlander, above, is homozygous for the other with a genotype of bsbs. The Newfoundland, at the right, is homozygous for the rarer brown mutation. His genotype is E/E, bc/bc. Dogs which are heterozygotes of any combination of these mutations would also be brown, i.e. bs/bd

    .

    Breeds in which brown dogs of with TYRP1 DNA changes have been detected

    The list of alleles may not be complete because relatively few dogs have been tested for some breeds

  •  

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