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Natural bobtail (NBT) is a naturally occurring mutation in the T-box gene resulting in a shortened tail. The mutation is inherited in an autosomal dominant fashion with both sexes being equally affected. This mode of inheritance means that presence of one copy of the mutant gene will produce the bobbed tail phenotype in males and females. The length of the bobbed tail is variable and under the influence of other as yet undetermined genetic factors that cause some NBT individuals to have nearly full-length tails while others may have virtually no tail. While heterozygous individuals (possessing one normal and one affected T gene) have shortened tails, data suggest that the homozygous condition (possessing two copies of the affected gene) is lethal in utero. Breeding of two carriers is predicted to produce 25% homozygous affected offspring thus a 25% reduction in litter size.
Genetic testing is recommended to verify and validate the natural bobtail status of dogs, especially if docking is allowed, and to help with breeding pair selection to eliminate the risk of reduced litter size.
Results reported as:
Test Result: Natural Bobtail
N/N Normal - no copies of the NBT mutation
N/BT Natural bobtail - 1 copy of the NBT mutation
BT/BT Natural bobtail - 2 copies of the NBT mutation*
Fawn/Sable, Tricolor/Tan Points, and Solid Black
(Fawn/Sable, Tricolor/Tan Points, Solid Black)
There have been four different alleles identified in a dog’s genes that signal the agouti coloration (this coloration can be exemplified as the coloration of the wild brown rabbit), also known as the A locus. If you’d like to learn more about the difference between an allele and a gene, click here. These alleles are Ay, aw, at, and a.
These alleles are dominant in a hierarchy. This means that Ay is more dominant than aw, aw is more dominant than at, and at is more dominant than a. For example, if a dog is Ay/at, the color associated with Ay will appear on the dog, rather than the color associated with at. However, this is all dependent on whether or not the dog carries the dominant black gene at the K locus or the recessive gene on the E locus. If a dog carries one or both of these genes, the A locus is muted and the agouti coloration will not appear on the dog. This is because both the K locus and the E locus are dominant over the A locus.
The agouti gene (A Locus) determines the base coat color in dogs that are ky/ky for dominant black. Dogs must be ky/ky in order to express any alleles on the A locus. The color of the dog can still be modified by other genes, such as by the B locus or D locus, however. For example, if a dog is b/b (recessive) for the B locus, they will still have areas that are pigmented as black. However, it will be modified to appear as a chocolate pigment.
However, if a dog’s A locus codes for the fawn coloration and the dog is b/b for the B locus, the fawn dog will have a chocolate nose. In contrast, a dog that is at/at will have a chocolate and tan coat, rather than black and tan. If a dog is n/n for the gene, that means that the dog is recessive for this gene and the typical colors associated with the pattern are not expressed. This is a generic term used to refer to the expression of any coat color.
The "Ay" Allele
The Ay allele is the most dominant of all four alleles on the A locus. The Ay gene produces a range of coat colors like light fawn colors, darker red colors, or even sable.
This variation of color is due to variances in the expression of this
gene. Dogs that are ky/ky for the K locus and have one or two copies
of the Ay allele will always express the Ay coat pattern. This is
because the Ay allele is more dominant than the ky allele expression.
It is important to note, however, that a dog can appear as fawn or
sable and could also carry any other of the three alleles. These
other alleles, however, would not be expressed, and a person
wouldn’t be able to tell the dog had the ability to produce other traits
based on looks.
This does not mean that the dog with a fawn coat (Ay) will always pass on a copy of the Ay allele or the coat color that the parent has. A dog that is Ay/aw, Ay/C, or Ay/a has a 50% chance of passing on the Ay allele and a 50% chance of passing on the other alleles. A dog that has two copies of the Ay allele will always pass on the Ay allele. As long as that dog is bred to another dog that is n/n (recessive) for the K locus, the dog will always produce fawn or sable pups.
The "aw" Allele
The aw allele produces a color known as "wild sable." This coat coloration is sometimes called the "wild type," or in some breeds, "wild boar." With this coloration, the hairs switch pigmentation from a black color to a reddish or fawn color. This color is sometimes seen in German Shepherds and other shepherd breeds. It is recessive only to the Ay allele. This also means that it is dominant to the at and a alleles, and will be expressed before the at and a alleles. If a dog is n/n for the Ay allele (meaning this allele is not expressed), a dog with one or two copies of the aw allele will express the aw coloration. A dog that is n/n for Ay and has one copy of the aw allele can carry either the at or a allele and not express them. However, even though the at and a alleles do not appear as a trait on the coat, either allele can be passed to any offspring.
The "at" Allele
Both the black-and-tan and tricolor phenotypes (expressed traits) are caused by the at allele. A tricolor dog is black-and-tan, with white. White is generally just an absence of color, rather than a pigment the dog expresses. For a dog to be black-and-tan or tricolor, he must be n/n for the dominant black gene (the K locus). This means that the K locus is not expressed, and
the dog will not be black. Furthermore, the dog must have either
two copies of the at allele, or have one copy of the at allele and
one copy of the a allele. The dog must be n/n for both the ay and
aw alleles in order for at to be expressed. This is because the Ay
aw alleles are dominant over at. A dog that is at/at will always
pass on a copy of the at allele to any offspring. This does not
ensure that the puppies will be black-and-tan. The coat color of
the offspring also depends on the genotype of the other parent.
There is also a "Mismarked Tricolor Pattern". Be careful as some breeders are willingly breeding these dogs. They have final made a connection with dogs testing NI on the Ralley gene and having and passing this.
The "a" Allele
If a dog is ky/ky on the K locus, the dog must be n/n for Ay, aw, and at in order for the dog to express the a/a coloration. A dog that is solid black with the recessive K locus must also have the recessive a/a allele in order to express the black coloration. It is important to make this distinction because a dog can also be solid black with kB/kB or kB/ky under the K locus. The A locus is not needed for this type of dog. Therefore, this type of black dog does not need the a/a coloration in order to express the black color. You can learn more about this type of dog by reading about the K locus or the B locus.
This is also the case for dogs that are bicolor and are negative for the K locus (ky/ky). This is generally the cause of a solid black German Shepherd. The a allele is sometimes referred to as the recessive black gene. Because this allele is the most recessive, for a dog to express this phenotype he must have two copies of the a allele and be n/n for Ay, aw, and at. A recessive black dog will always pass on the a allele to all offspring.
Dilute Coat Color D-Locus and New D2-Locus Description:
The MLPH gene codes for a protein called melanophilin, which is responsible for transporting and fixing melanin-containing cells. A mutation in this gene leads to improper distribution of these cells, causing a diluted coat color. The mutation causing color dilution is recessive, and two copies of the mutated gene (the D allele or the D locus) are needed to produce the diluted coat color.
The MLPH mutation affects both eumelanin and phaeomelanin pigments. These pigments control the color of the dog. Black, brown, and yellow dogs can all be affected by the D locus. However, the effects of the dilution are more pronounced in black dogs. A diluted black dog becomes known as a blue dog. Names for this color trait vary across the different breeds, with blue, charcoal, slate, or grey being common names. A diluted chocolate dog is often referred to as a lilac or isabella and a diluted yellow dog is offten called champagne. Dogs that express the diluted phenotype have a d/d or d2 genotype. They are coded as B/B, B/b, or b/b and E/E, E/e, or e/e respectively, with regards to the E and B loci, which determine coat color.
Because the mutations responsible for the dilution phenotype are recessive, a dog can carry one of the two dilution variants and still express a normal coat color. These dogs can pass on either the full-colored genes or the diluted traits' alleles to any offspring. This means that two dogs that are full-colored can have a diluted puppy. This makes DNA testing for the D locus an important breeding tool, whether breeding for a dilute coat, or to avoid it.