 | Dilute Gene
*** JUST SAY NO TO "SILVER" LABS
The American Kennel Club (AKC) (and all other reputable kennel clubs around the world) recognizes three coat colors in the Labrador: black, yellow and chocolate. These colors are inherited based on genes at two loci: B and E. In recent years, other colors have become more prominent in the breed. Breeders refer to these colors as ‘silver’, ‘charcoal’ and ‘champagne’. In order to obtain these new colors, a recessive D locus dilution factor (d) must be introduced into the population. According to literature, the dilution factor was not originally a part of the Labrador Retriever breed, and therefore, controversy surrounds the topic.
Information known about the dilution factor’s lack of presence in the Labrador suggests that it was introduced into the breed in the United States, at some point in time, probably in the late 1940s, early 1950s, by crossbreeding. Research has shown that some dogs with coat color dilution are prone to hair loss and reoccurring skin problems. These conditions should be selected against by eliminating dilution factors within the Labrador population.
The Labrador Retriever breed should be consistent with its breed standard, and dilute colored dogs incorrectly represent the purebred breed.
The Labrador Retriever breed, as it was developed and registered in the United Kingdom, never (until 2006) carried the dilution factor. A survey in the United Kingdom, Europe, Canada and the United States shows that no reputable Labrador breeder has ever had a puppy carrying the dilution factor, so it is hard to explain the direct cause of a mutation in the breed. There is no other explanation than that crossbreeding occurred with a breed carrying dilution, probably the Weimaraner, and they passed the d allele down to offspring.
There are many breeders in the United States who specialize in breeding diluted “Labradors”. Diluted dogs typically have a metallic-looking sheen to the hair. A typical Labrador with a black phenotype can have the genotype: BBEE, BBEe, BbEE or BbEe. A Labrador with a chocolate phenotype will have either the bbEE or the bbEe genotype. A dog displaying a yellow coat must have the homozygous recessive genotype at the E locus, and therefore can be BBee, Bbee or bbee. It is possible for these genotypes to be diluted if the dog carries two copies of the recessive dilute gene, dd. Dogs that carry at least one D will not have a diluted coat. If a dog carries the Dd genotype at the D locus, one copy of the dilute gene is present. If bred to a bitch carrying a dilute gene (Dd or dd), diluted offspring could be produced.
Health problems and misconstruing of breed standards due to dilution
Various expressions of the dilution gene have been noted. Some dogs with dilute color display minimal or no health problems; other dogs experience hair loss and skin problems. Color dilution alopecia (CDA) and black hair follicular dysplasia (BHFD) can accompany coat color dilution. These diseases cause recurrent skin inflammation and drying, bacterial infections of hair follicles and severe hair loss. Late 2013 a 12-week-old female silver Labrador Retriever was submitted to the Comparative Ocular Pathology Laboratory of Wisconsin, and was diagnosed with Malignant Uveal Schwannoma. Scientists believe that the dilute color mutation may contribute to the cause.
Other disorders that could travel with the dilution gene are heritable Weimeraner genetic issues such as trembling disorders, autoimmune related vaccination sensitivity and intolerance, Von Willebrands Disease, hyperuricosuria causing painful bladder and kidney disease, and behavioral problems that are more common in the Weimaraner, such as separation anxiety, and dominant, protective, territorial temperament. Minimizing occurrence of these conditions would mean minimization of the dilute mutation. Selection against dilution is important in breeds that display health issues associated with the mutation. It is also important to minimize the dilution mutation in breeds that do not have a standard written which include these colors. The Labrador Retriever is currently one of these breeds. Dilute colored Labrador retrievers are a disqualification according to breed standards. Those dogs carrying the dilute gene should not be registered as purebred Labrador Retrievers.
The Labrador Retriever Club Inc. is the AKC Parent Club of the Labrador Retriever. On May 12, 2014, the LRC published the following message on their website: “Very exciting news – the OFA has agreed to maintain a database of Labradors who have been permanently identified (microchip or tattoo ) and have been tested for the d gene. Dogs having the genotype dd will be listed as affected, Dd as carriers of the dilute gene and DD as clear of the dilute gene. This is great news for us.”
Note: The Orthopedic Foundations for Animals (OFA) only registers hereditary diseases (or the lack of those) in their databases. So it’s not a simple matter of “a different colour”.
Implications
Although findings of these various studies do not definitively explain the cause of dilution in dog coat colors, they help us to understand the correlation between dilution and the MLPH gene. Knowledge that the MLPH gene mutation is responsible for dilution has allowed DNA testing companies to begin testing for the mutant dd allele. These tests can help identify carriers of the d gene, and therefore, can help to eliminate it from populations, such as the Labrador retriever, in which it is undesirable. Responsible breeders should take the time, and spend the money, to have their breeding stock genetically tested at the D locus. Labradors displaying dilution, ‘silver’, ‘champagne’ or ‘charcoal’, coloration (dd) should not be used for breeding. Ideally, only Labradors with genotype DD at the dilution locus should be used for breeding.
Throughout the years, Labrador breeders have worked diligently to eliminate undesired traits and illnesses in the breed. A complete elimination of coat color dilution in the Labrador retriever would take a very long time, through DNA testing and breeding stock selection. Kennel clubs and breed clubs are expected to respect the breed standard and the closed character of the studbooks. No respect of the breed standard and the closed character of the studbooks is shown by the common practice of registering “silver” as chocolate, “charcoal” as black, and “champagne” as yellow. Labrador retriever breeders are equally expected to follow the breed standard as currently written when selecting parents for future litters.
The situation in Europe
The AKC registration of “silver”, “charcoal” and “champagne” dogs as chocolate, black or yellow Labrador Retrievers, without any restrictions, has resulted in the disturbing fact that in 2011 the first American dilutes were imported into the United Kingdom, and that these dilutes were registered by The Kennel Club, also without any restrictions. As a result, hundreds of dilutes were born in the United Kingdom, and most of them were registered by the K.C. as completely normal black, chocolate or yellow Labrador Retrievers. The Kennel Club told the Labrador parent club that “DNA-tests” proved that these dogs were purebred Labrador Retrievers, and that there was nothing they could do about it.
The Kennel Club did not mention when these “tests” took place. However, it’s a matter of fact that these tests are extremely unreliable. Yes, the tests could show that the parents and grandparents of a certain dog are Labrador Retrievers, but does that make a dog a purebred Labrador? Even the most modern and sophisticated tests are not able to say something about anything that happened more than three generations ago, while many dilutes have a history that goes back to the 1970s, or even to the 1950s.
So, instead of using an extremely unreliable test to “prove” that a Labrador is purebred, the K.C.’s should use a test that is reliable: any dog carrying the d-gene can not be a purebred Labrador Retriever and should be excluded from the registry.
TESTING SUMMARY
The D Locus (Dilute) coat color test reliably determines if a dog has one of the following genotypes at the D locus:
D/D
This dog carries two copies of D which does not result in the "dilution" or lightening of the black and yellow/red pigments that produce the dog’s coat color. The base coat color of this dog will be primarily determined by the E, K, A, and B genes. The dog will pass on D to 100% of its offspring.
Interpretation: Non dilute
D/d
This dog carries one copy of D and one copy of d which does not result in the "dilution" or lightening of the black and yellow/red pigments that produce the dog’s coat color. The base coat color of this dog will be primarily determined by the E, K, A, and B genes. The dog will pass on D to 50% of its offspring and d to 50% of its offspring.
Interpretation: Non dilute (Carrier)
d/d
This dog carries two copies of d which results in the "dilution" or lightening of the black and yellow/red pigments that produce the dog’s coat color. However, this variant modifies or "dilutes" the base coat color of the dog that is primarily determined by the E, K, A, and B genes. The dog will pass on d to 100% of its offspring. |
Date(s): October 22, 2016. Album by Green Acres Angels. 1 - 2 of 2 Total. 0 Visits. |
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