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MERLE AND BRINDLE COLOR GENETICS
NOTE: We absolutely do not condone breeding just for color!
The Merle aka Dapple is a pattern and not a color in a dog's coat, and is usually a solid base color (black or red/brown) with lighter blue/gray or reddish patches, giving a watercolor effect, and an uneven speckled or mottled appearance.
WHAT CAUSES MERLE?
Merle is carried by a genetical change in the Silver-Gene (SILV, Pmel17). This is a mobile genetical element (Retrotransposon), that lays within the SILV-Gene and interrupts its functionality. The merle color responsible for the defect SILV-Gene is named with M while the normal SILV-Gene is named with m. The merle originates in dogs that carry this mutant version of a SILV-Gene heterozygous (Mm). The defect SILV-Gene (M) shows an imperfectly dominant heredity.
DEFINITIONS OF THE MERLE GENE:
M(c)m: Non-merle (heterozygote, cryptical“ merle)
heterozygote- A pair of genes where one is dominant and one is recessive-they're different. Like all words with the prefix hetero, this has to do with things that are different - specifically, genes If you inherited the same gene from both parents, it's homozygous - the same.
M(c)M(c): Non-merle (homozygote, cryptical“ merle)
homozygotes- An organism with identical pairs of genes with respect to any given pair of hereditary characters and therefore breeding true for that character.
Origin of homozygote.
M(c)M: Merle (heterozygote, cryptical“ merle)
Due to the unstable and variable nature of the merle gene, sometimes merles have patches that are only partially diluted and are between the base and the patch color. These are known as dilute spots, and they may sometimes appear brownish. Harlequin is a modified type of merle where the areas between the patches are diluted completely to white.
Dilute spots don't have anything at all to do with the Dilution gene (d) and are just a normal variation of the merle pattern.
Dogs which carry the merle-gene (Mm; one normal and one mutant gene) will give the merle gene with a similarity of 50% to their offspring.
Definition of Allele: Alleles are forms of the same gene with minimal differences in their sequence of DNA bases.
Hidden Merle: Hidden Merles are merle dogs who do not exhibit any merle pattern because their coat color does not show the pattern (Merling is not normally shown in red, gold, fawn and cream coat colors). The hidden merle can be distinguished only by a genetic test.
Cryptic Merle: aka "Phantom" or "Ghost" merles have little, if any, visible merling because their patching is so heavy. Sometimes a recessive red merle will have blue or partially blue eyes, but otherwise, there may be no indication that the merle gene is present, in some cases it is not visible at all. The dog can have only small patches aka "points" of merle, for example, at the base of their tail or ear, or the merle coloration can be hidden by white markings. Assumably, these dogs carry a specific shorter mobile element in the SILV-Gene, sometimes one copy, sometimes two, a stabile genetical reversion, which means a spontaneous loss of the disposition merle (M) ín the offspring of merle gene carrying dogs is documented in the medical literature by a percentage of 3-4%. Unlike regular merle dogs, in the cryptic merle dogs, no serious health problems are connected with the regular (not shortened) merle allele have been described. They apparently have no eye or hearing problems. Dogs with two copies of cryptic merle gene (Mc/Mc genotype) or dogs with one cryptic merle copy and one regular merle copy (M/Mc genotype) have no health problems. The correct description of cryptic merle is a problem when registering the dog. These dogs appear like normal colored dogs.
The other main way that merle can be hidden is through the recessive red allele ee. Recessive red dogs are unable to produce any eumelanin pigment (The most common type is eumelanin, of which there are two types—brown eumelanin and black eumelanin. Pheomelanin is a cysteine that contains a red polymer of benzothiazine units largely responsible for red hair, among other pigmentation.) in their coat, making them solid red (phaeomelanin). Phaeomelanin cannot be merled, not in a heterozygous merle. A recessive red dog with the merle allele will just appear to be a normal clear red. Even if it's rare, but there are dogs which do not show the merle color but still carry the merle gene and when bred, their offspring can be merle.
This Cryptic merle (merle only visible going across her right shoulder blade) Alapaha puppy pictured above, displays a butterfly nose with a blue right eye and the left eye is referred to as a "Split eye". The "Split eye" has some blue in it and the rest is brown or amber. Split eyes vary from mostly blue to mostly brown or amber. Walleyes, technically known as heterochromia, are when a dog has one blue eye and one brown or amber eye. Other terms for the various eye coloration includes marbled, fleck, glass-eyed and odd-eyed.
Nose: The random coat dilution caused by merle also affects the eyes and nose. The eyes can be completely or partially blue and the nose may be completely or partially pink, known as a "butterfly" nose in merles. Not all merles have blue eyes or pink noses though, and merles with heavily dark patching are more likely to have a normal eye and nose pigment.
POSSIBLE GENOTYPE COMBINATIONS:
mm = non-merle
mm = non-merle
(Non-Merle) 100% of these dogs are mm- Carry the full pigment coating of the fur.
A solid black (no merle), is mm and can only give her pups a solid color gene.
mm = non-merle
Mm = merle
50% of these dogs are Mm = merle
50% of these dogs are mm = non-merle - Carry the full pigment coating of the fur
mm = non-merle
MM = double-Merle
100% of these dogs are Mm = merle
Mm = merle
25% of these dogs are mm = no merle - Carry the full pigment coating of the fur
50% of these dogs are Mm = merle
25% of these dogs are MM = double merle
(Merle x Merle) - This is the litter where the double merle pups show up. You will get solid color pups since each parent still carries a solid gene.
CR/CR = Double Cryptic Dog carries two copies of the Cryptic "CR" allele.
m/CR = Merle Dog has one copy of the Cryptic "CR" allele and one negative "m" copy of Merle allele. The dog can pass either allele on to any offspring.
m/m = Negative Dog is negative for Cryptic "C" allele. The dog will always pass on a negative copy of the Merle allele to all offspring.
M/CR = Merle/Cryptic Dog carries one copy of the dominant "M" allele and one Cryptic Merle allele. The dog is considered a Merle and carries Cryptic Merle. The dog can pass either allele on to any offspring.
All Genes Come In Pairs:
Genes can be "dominant" or "recessive." A dominant G gene is always visible, no matter what it is paired with. A recessive G gene is only visible when the other half of the pair is the same recessive (homozygous G).
Dominant genes are not always "good" and recessive genes are not always "bad" (nor is the opposite true).
Merle (M) is dominant to solid (m).
Black (B) is dominant to red (b), and there is no visual clue to know if a black dog is carrying a red gene (although there is a DNA test that can be done).
Merle is a single gene. It can be combined with another merle gene (creating a double merle dog), or a solid gene (creating a normal merle).
Merle can cause lack of pigment in certain vital areas such as the eyes and inner ears. Most heterozygous merles have plenty of pigment because they still have an m (non-merle) allele to help them to make it, but double merles often have large white areas where there is no pigment produced at all.
Dogs which carry the heterozygous mutant version of the SILV-Gene (MM, Double Merle), are mostly colored white or have great white areas on their body. These kinds of dogs can have very severe damage and malformations to the eyes which can cause blindness, and the internal ear which can lead to deafness. Dogs that are DOUBLE MERLE SHOULD NOT BE BRED!
Genotype - Term coined by Danish botanist, plant physiologist and geneticist Wilhelm Johannsen in 1903 – is the part (DNA sequence) of the genetic makeup of a cell. Therefore, of an organism or individual, which determines a specific characteristic (phenotype) of that cell/organism/individual.
Phenotype - (Physically Visible) (from Greek phainein, meaning 'to show, and typos, meaning 'type') is the composite of an organism's observable characteristics or traits, such as its morphology, development, biochemical or physiological properties, behavior, and products of behavior.
Brindle (DDKK) - Brindle is a coat pattern and not a color, and has a wild-type allele which is the product of at least two recessive genes and is rare. Many red breeds carry the brindle gene but it is not expressed unless the animal has a wild-type allele. Dogs must inherit the recessive brindle gene, usually from both parents that visibly show this pattern, or both having it close within their heritage for the brindle to be outwardly expressed. Sometimes, brindling is not that noticeable. The gene might cause the dog to be brindled all over or just points such as around their ears or base of their tail.
Fawn, blue, harlequin, brindle, chocolate and piebald are all recessive genes that can be carried in any color. The brindle can also carry unseen colors. Merle and black are dominant genes. A blue merle has two blue genes as well as one merle but can carry others as well. Read more on Brindle.
K-locus - Dominant Black - Description: Coat coloration is controlled by several different genes in dogs. Dominant black is due to a mutation in a Beta-defensin gene (CBD103). This gene fawn colors in certain breeds.
KB/KB - The dog carries two copies of the dominant "KB" allele. The dog will not have fawn offspring. The dog will always pass on a copy of the "KB" allele to all offspring.
KB/n - One copy of the dominant black allele was detected. The agouti phenotype will be altered and in some breeds can result in brindle. The dog could pass on this allele, or either the brindle or fawn allele, to any offspring.
n/n - The dog does not carry the dominant black mutation. The dog's coat color will be determined by the agouti gene and may pass on brindle or non-brindle.
The dominant black gene consists of three different alleles or variants. The first allele, which is dominant, is notated as "KB," or dominant black. The dominant black allele is actually a mutation that reduces or eliminates the expression of the agouti gene. Because this mutation is dominant, a dog only needs to have one copy of the mutation to affect the agouti locus.
The second allele is known as the "brindling" allele, and is represented as "Kbr." The Kbr allele is a separate mutation that still allows the agouti gene to be expressed but causes brindling of the agouti patterns. The agouti gene represents several different colors, such as fawn/sable, tricolor, tan points, or recessive black. The Kbr allele is recessive to the KB allele, however, it is dominant over a third allele, Ky.
The third allele is represented as "Ky". This allele allows the agouti gene to be expressed without brindling. When a dog is Ky/Ky at the K-locus, the agouti locus determines the dog's coat color. For example, a dog that is Ay/Ayat the agouti locus could be fawn/sable. If that same dog is KB/KB at the K-locus, the agouti locus will be hidden, and his coloration will be determined at the B and E loci. However, if that same dog is Ky/Ky at the K locus, he will then be able to express agouti and will be fawn/sable.
At this time, there is no direct test for the "Kbr" allele, although it can generally be inferred through testing for the presence of the dominant black allele, as well as through phenotypes of the parents and offspring. Testing for the dominant black mutation determines if the dog is able to express agouti phenotypes. However, it is limited in that it will not tell you if the dog will pass on brindle.
D-Locus = (Dilute Coat Color)- Chocolate Dilute Basic Color Description
B/B or B/bD/D = Black
B/B or B/bd/d = Blue
b/bD/D = Liver/Chocolate
b/bd/d = Lilac
e/ed/d = Champagne