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Old 02-21-2012, 01:58 AM   #46 (permalink)
 

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I have a RE/Gotti lined black pup that has a white spot on his chest that also has ticking in it. Although, as for someone's statement that the merle gene is dominant and that you can have a merle pup throw a black and then that black throw is merle is inaccurate. If the merle gene is truly dominant, it will show itself over black and no other color can "hide" the merle gene. Dominant genes are never hidden. This is just a little something I've picked up from dealing with equine genetics. Hope that helped a little.
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Old 02-23-2012, 11:24 PM   #47 (permalink)
 
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Quote:
Originally Posted by Chaqida View Post
I've got an White and Coco Fawn Ticked APBT pup. He seems to grow more spots as he's gettin older. This is him when i first got him at 4months

And this is him at 7months
Did you mean 4 weeks and 7 weeks?
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Old 02-24-2012, 01:11 AM   #48 (permalink)
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Quote:
Originally Posted by kybully2012 View Post
I have a RE/Gotti lined black pup that has a white spot on his chest that also has ticking in it. Although, as for someone's statement that the merle gene is dominant and that you can have a merle pup throw a black and then that black throw is merle is inaccurate. If the merle gene is truly dominant, it will show itself over black and no other color can "hide" the merle gene. Dominant genes are never hidden. This is just a little something I've picked up from dealing with equine genetics. Hope that helped a little.
You are wrong.. Merle is dominate however you can also have "Cryptic" Merles, sometimes referred to as Phantom or Ghost merles...In this case the merle gene IS present but hidden.. In baby terms.. Perhaps before you tell me i'm wrong, or anyone.. You should learn about the subject first.. Not to be insulting but rather, common sense..

The M locus is the home of the merle gene. Merle is dominant, and so denoted by the capital letter M. Non-merle is recessive, and denoted by m.

Merle is pretty unique because all merles are heterozygous (Mm or mM). A homozygous merle is actually a double merle, similar to the lethal white gene found in horses and other mammals. Click here to go to the page on double merle.

The merle gene dilutes random sections of the coat to a lighter colour (usually grey in a black-pigmented dog), leaving patches of the original colour remaining. The patches can be any size and can be located anywhere, unlike the patches on a piebald dog (which are generally confined to the body and head). The edges of the patches appear jagged and torn.

Merle affects eumelanin. That means that any black, liver, blue or isabella in the coat will be merled, whether it's the whole of the body, a mask on a sable, shading, brindle stripes, or even a saddle. Phaeomelanin (red) is not affected at all and will appear as normal.

The pictures above show the range of markings found in merles. The first dog has very few black patches, and they're mainly quite small. The second dog shows the normal merle pattern - a mixture of larger and smaller patches, covering roughly 50% of the body. This pattern is generally the most preferred in breed standards. The third dog has very large black patches, sometimes referred to as blanketing. The last dog is known as a minimal merle. It is almost completely black with just a very small amount of merling on its ear and tail. This pattern is rare and generally discouraged because it can "hide" the merle gene if the black covers up all the merle in the coat. Dogs with little or no visible merling are sometimes called cryptic merles.

The dogs above are called "blue merles" because of the bluish colour between the patches in their coat. This is a widely-used term but is actually misleading. Technically they should be "black merles". Their nose pigment is black and their eyes are brown. They are able to make normal eumelanin in their coat, so their patches are black. If they didn't have the merle gene, they would be solid black. "Blue merle" is misleading because it seems to say that these dogs have blue pigment (dd acting on black), when in fact they have black.

An example of the genotype of one of the above dogs would be: BBCCDDEEggMmSSKK (most of these aren't necessarily homozygous, but I will assume they are for ease, otherwise I'd have to keep saying, "KK, kK or Kk" etc). The genotype translates as: no liver colour (BB), no albino factor (CC), no dilution (DD), no mask or recessive red (EE), no greying (gg), merle (Mm), no white spotting (SS), and solid black (KK).

Merle and the APBT..


The recent appearance of merle patterned APBTs and a couple breeders specializing in the "new" and "rare" color pattern has stirred up a controversy in the APBT community. The general thought among those that have been around the breed for the greatest number of years is that, these new color patterns were brought about by unscrupulous outcrossing to a separate breed such as Catahoula Leopard dogs. Several breeds are known to carry merle as a color pattern but the APBT is not one known to have ever carried this "infected" allele. What is known is that Catahoula Leopard dogs along with pit bulls are often used in the sport of hog catching and it is known that crosses of these breeds have been made in attempts to produce more competitive catch dogs.

The following c omments from the APBT standard committee provide prelude to a brief essay on the merle locus in relation to the APBT

Walt Pasko "I feel the emergence of the merle color pattern in our breed has raised the questions of how it was introduced into our breed and what health problems the merle gene could cause. From all information I've read, I have to recommend that the merle color be made a disqualification in the APBT Breed Standard."

Carol Gaines Stephens "I strongly oppose the color pattern 'merle' in the APBT since it has never been there in the past and has just recently risen it's ugly head with the popularity of the catch dogs in the south. I have spoken to several people from the south that say that they know and do so themselves, cross the APBT with the Louisiana Catahoula Leopard Dog to make a better catch dog. If the gene has never been present in all these decades/centuries then how did it finally come about just recently? I am a firm believer in leaving the standard the way it was originally, but when something surfaces that has no rhyme nor reason, then I think we have to address the matter."

Cheryl Larum "I am in agreement with the other committee members on the merle issue"

Scot E. Dowd " First it should be noted that there are ways that the merle can remain hidden such as within a complete phaeomelanic coat where the merle would not be evident, also there are cryptic merles, however this absolutely would fail to explain the relatively recent appearance of this color pattern in the APBT. I feel that another allele with defined health problems associated with this locus, is not a positive thing for our breed"

The following information is submitted on behalf of the NAPBTA standard committee - Scot E. Dowd

There are two issues of concern with the merle as a color pattern. The first, as mentioned, is that merle pattern in the APBT may have come about through unethical outcrossing to another breed of dog. This practice would then have been followed by falsely registering such a outbred animal either with the ADBA or UKC as a purebred APBT. Such false registration would be termed hanging papers. The other issue is related to the health aspects of the Merle allele. Here I will try to answer the predominant questions that arise regarding the merle allele and the APBT without making a judgment of my own other than that expressed above.

Why is a color or color pattern so important to the stewards of the breed?

The entire process of coloration and color patterns in dogs starts with embryonic development. The specific cells that become melanocytes (pigment producing cells) are derived entirely from the neuronal crest of the embryo. This essentially means that pigment cells are directly produced along with the same cells that give rise to the nervous system. Though not entirely true, it can be assumed that if you have defects in genes associated with color genetics you might also have nervous system defects because both types of cells are derived from the neuronal crest. This provides a logical genetic indicator and explains why it is likely that certain dilute or patterned dogs, such as extreme piebalds, or other types of homozygous dilutes common in the APBT, as well as those that may be carrying the Merle pattern are prone to psychological, neurological and/or immunological problems found in other breeds that carry these alleles.

What is merle?

Merle like other dilution alleles acts to lighten whatever color would otherwise have been expressed. However, with merle the lightening effect is not spread evenly over the coat, but produces patches of undiluted color (dappled pattern) scattered over the dog's body. The merle gene when heterozygous Mm (only one copy of the gene) on an otherwise black dog produces a blue merle which is phenotypically a bluish gray dog that is dappled with full color black spots. A homozygous or MM dog (carrying two copies of the merle gene), often called a double merle or a homozygous merle, will be a mostly white dog (similar to an extreme Piebald). The normal state of the merle locus is dual recessive mm and completely lacks the offending transposon resulting in normal color.

Maybe merle has been in the breed throughout its history and only now is it being noticed?

The response to this question is also genetic in nature. The genetic and phenotypic nature of the Merle locus and the merle allele (M) is such that it would not remain unnoticed in a breed and suddenly appear. It would take crossing to another breed that carries the merle allele for it to be transferred into the breed. The reason it could not remain invisible or hidden is because the Merle allele is expressed with incomplete dominance. This means, if it is within the genome at all, even in a heterozygote (one copy of the gene) state, it is still expressed and evident. The M allele is not found in all breeds; in fact most breeds do not carry it. Finally, this specific transposon cannot arise spontaneously or through mutation as some have claimed.

What are the health problems associated with the merle allele?

The merle allele like a couple other dilution factors when expressed in a homozygous state is correlated to psychological, neurological, and usually immunological issues. Here I will mention a few of the issues. The first are eye development problems that are superficial in nature affecting appearance such as heterochromia iridis (A difference of color between the iris of one eye and the other), thus a dog with one brown and one blue eye has heterochromia iridis. Note that this defect is not necessarily or always indicative of having the merle gene because it can also be found in dogs with extreme piebald or double blue dilution for example. In addition to superficial indicators there are also major effects such as absence of tapetum lucidum. Tapetum lucidum is a reflective substance that lines the back of the dogs eyes. This reflective structure acts like a mirror and reflects light back through the retina, like a satellite dish giving the retina two chances to catch the light. Dogs that lack tapetum licidum have night blindness or reduced ability to see in low light. Another defect is lack of retinal pigment and microphthalmia. Microopthalmia (smaller than normal eye) is described as dogs having prominent third eyelids and seemingly small eyes which appear recessed in the eye socket (enophthalmos). Another problem known as coloboma is actually a physical cleft in a portion of the eye, particularly the iris . In addition to the eyes which are a key indicator of neurological defects, there is also evidence for effects on the ears that result in reduction in auditory sensitivity or complete deafness because the merle color locus exerts epistatic effects on ear development. Excessive white or dilution in a dog of any color can be a warning sign of potential hearing problems. If there is no pigment in the inner ear the dog will be deaf; white ears are more likely to lack inner ear pigment.

More technically, what is the genetic explanation of the merle pattern?

The merle allele is considered to be caused by a transposon or transposable element. A transposon is a piece of DNA that has the potential to actually jump out of, or excise from the gene it has infected (disrupted), during cellular division and genetic DNA replication. This means that while melanocytes are migrating from the neuronal crest during embryonic development the merle transposon can remove itself from the gene in some of the melanocytes when they are derived and produce normal coloration on those parts of the coat to which they migrate. Thus, the merle allele acts to cause eumelanic areas in the coat, to become diluted, but other areas to be fully and intensely pigmented. Such fully colored areas occur in scattered patches throughout the body. The merle locus is autosomal (not carried on one of the sex chromosomes) acting as a dominant mutation (it is expressed in all dogs that carry this gene). It should also be noted that genetically such transposons do not arise spontaneously but must be passed from sire and/or dam to offspring. This means that if the APBT did not carry this allele to begin with, then only through outcrossing to another breed, that does carry this transposon, could it be integrated into the APBT genome.

Thus, we as members of the National American Pit Bull Association are presented with the issue of a dilution pattern that may have been introduced into the breed by unethical conduct. As stewards of the breed we have to choose to continue to honor our current standard and allow this color pattern or to change the standard to reflect that merle is not an acceptable color pattern for the breed.
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Last edited by KMdogs; 02-24-2012 at 01:38 AM.
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Old 02-24-2012, 01:31 AM   #49 (permalink)
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by Amy Greenwood Burford B.S.

One of my responsibilities as a member of the staff of the American Dog Breeders Association is to be the ‘color expert’. I believe that my many years of experience in the breed, as well as the opportunity to have grown up in a true ‘American Pit Bull Terrier’ family. has given me the exposure that it requires to know the descriptive terms to describe the many diverse colors in our breed. The color description that is placed on your ADBA registration papers does not in any way attempt to depict the genetic makeup (genotype) of the individual dog. Instead it is a description of the dogs actual color that you see (phenotype). This color description is used for identification only and in many cases does not predict what color combinations the individual dog will produce in its offspring.
Over the course of the last few months, I have received a surprising number of questions concerning color and the genetic inheritance of color. Questions such as: 1. The blue color in the APBT in the past was very rare. How are so many kennels now producing blues in such numbers? 2. It is possible to produce a puppy with a black nose, when both parents have red noses? 3. Where does the chocolate coloring come from? 4. How did I produce a brindle from a line that has never had brindle dogs? In my review of the genetics of color in the American Pit Bull Terrier, I will review a few of the principals of genetic inheritance in general and look at the research that has been done in the field of color genetics in our breed in an attempt to give our readers a better understanding of color genetic as well as provide answers to the above questions.

GENETIC PRINCIPALS
Each offspring inherits one half of their genetic make-up from their sire and one half from their dam. All members of the genus canis, to which all dog breeds belong have 78 chromosomes. They appear in pairs and consist of chains of DNA material. Small sections of these DNA chains make up genes, the genetic code for the production of certain proteins in the individual dog. The genetic material for particular traits in the dog are located in certain regions on the chromosomes called loci (plural) or locus (singular). The different assortment of genes that are possible are a particular locus are called alleles. In many different breeds, through selective breeding, only one allele is found at a particular loci, leading to all members of the breed having the same trait. This is why purebred dogs will breed true, for those characteristics that distinguish one breed from another. Alleles exhibit a dominance relationship when paired with a different allele. When the alleles are different at the same loci, they are said to be heterozygous. When the alleles are alike at the same loci, they are said to be homozygous. Dependent upon how many different alleles are possible there are multiple combinations of dominance. The term epistatic (above), means more dominant and hypostatic (below) means less dominant. Geneticists use an upper case letter: example (A), to signal a dominant allele, and a lower case letter: example (a) to denote a recessive allele.

The study of color genetic within a breed can be complex, as there are nine different locations (loci) on the chromosomes that effect the final color that you see in your dog. At each loci are two or more alleles, or gene choices, that interact according to their dominance-recessive relationships. At loci that have more than two alleles, the relative dominance in the series have been listed in order of their dominance.
Genetic research into the genotypes of coat color has not been done with UKC or ADBA registered APBT. The reason is this: throughout the history of our breed, dogs have not been bred for color. All colors were considered equal. An individual dog was selected as breeding stock based upon a multitude of factors, none of them being color. The canine genetic research into the genotype of color has been done solely in AKC registered breeds. One of the breeds that has been studied is the American Staffordshire Terrier. As a matter of review, it is important to understand that every dog accepted into the AKC registry as an American Staffordshire Terrier was also registered with the UKC or ADBA as an American Pit Bull Terrier. The year was 1936, and the popularity of the Our Gang Comedy and show’s mascot, Petey, prompted the AKC to open their stud book to the breed as long as the breed name could be changed to the American Staffordshire Terrier. No other breed has been crossed into the AKC American Staffordshire Terrier lines, so we are justified in examining the results of this research and applying it to our ADBA registered dogs. The researched results of the color genotypes possible in our breed, at the nine loci responsible for the determination of color are presented below:
As/Ay/at, B/b, C, D/d, E/Ebr/e, g, m, S/si/sp/sw, t

Locus A Series: Dark Pigment Pattern
This locus has six different alleles possible in the canine population. Only three are present in the APBT breed.
(As) dominant Black
(Ay) dominant Yellow
(at) bicolored pattern (tan ‘Doberman like’ markings on a solid coat)
The A alleles are pattern factors that control the amount and area distribution of dark and light pigment. They act within the hair follicle to switch pigment synthesis between light and dark. It is important to remember that alleles at this locus interact with Locus E alleles.
(As) - DOMINANT BLACK: This allele produces uniform coverage of dark pigment over the entire body. Its action is expressed in all dogs with black or brown coats. The (As) allele is almost completely dominant over others in the A series. The black color ranges from pure black to a black with a brownish cast (seal). Geneticists are uncertain if the allele is incapable to produce pure black without additional help from another locus, or if the brown cast indicates a heterozygous allele.
(Ay) - DOMINANT YELLOW: The (Ay) allele restricts dark pigment, producing yellow colors. When homozygous, the coat can be clear gold, but often has black tipped hairs, especially on the head and down the back.
(at) - BLACK AND TAN PATTERN (BICOLORED): The typical tan points are above each eye, on each cheek, on the lips and lower jaw, extending under the throat, two spots on the chest, below the tail, and on the feet to the pasterns and hocks, extending up the inner sides of the legs. These tan points can occur on black or seal, blue, chocolate or red solid colored dogs. A great deal of variation can occur with these tan points, even within the depth of the pigment. In some dogs the tan points are not always marked and the color contrast is not always distinct.

Locus B Series - Black/Brown Pigment
(B) black pigment
(b) brown pigment
This locus contains only two alleles, the dominant (B) producing black skin and nose pigment and the (b) recessive allele, producing brown pigment. In dogs that are red or buckskin, the Locus (B) alleles are expressed in skin color, most visible around the eyes and nose. The black nose indicates the genotype is (BB) or (Bb), both which would be expressed as black nose because of the dominance of the (B) allele. A light brown or red nose is (bb), or homozygous recessive. Being homozygous recessive, both parents must contribute one recessive (b) gene to the offspring to produce the red nose. When breeding two dogs with the (bb) genotype, the only resulting combination in the pups would be ( bb) or red nose.

Locus C: Pigment depth
The Locus C series controls the production of pigment throughout the coat. In dogs, the expression of the Locus C alleles is based on observation rather than experimental studies. The American Staffordshire Terrier breed is felt to have only the dominant (C) allele at this locus. The C allele allows the full expression of color, of dark and light pigments. The allele (cch) or Chinchilla Dilution, found in other breeds at this locus, causes the light pigments to be diluted out in various degrees. This would account for the varying shades found in many littermates depending on their homozygous or heterozygous pairing. The chinchilla dilution allele (cch) does not affect the dark pigment, thus allowing for the white dog with black skin pigment and black nose. Other researchers (Robinson) feel that other modifier polygenes are responsible for this phenotype.
CC full color
Ccch medium shade
cchcch pale shade

Locus D pair: Pigment density
(D) intense pigment density
(d) dilute pigment density
The locus D pair modifies the density of the pigment. The dominant (D) gives full density in both the heterozygous (Dd) or the homozygous (DD) combination. The homozygous recessive (dd) alleles dilute the color. When the dogs basic color is produced by dark pigment, genotype (Bbdd) or (BBdd) yields the color known as blue. The black coat is modified as well as the skin pigment to a gray or blue pigment around the eyes, pads and nose. When the dogs basic color is produced by a light pigment the genotype bbdd (dilute brown pigment) produces a fawn with a silvery cast known in our breed as a fawn/bluies. The skin pigment around the eyes is flesh colored as well as a red or brown colored nose.

Locus E Series: Extension
(Em) black mask
(Ebr) brindle

(E) extension of dark pigment

(f) restriction of dark pigment
The Locus E alleles affect the extension of dark pigment, and all of the alleles at this locus interact with those of locus A.
(Em) - BLACK MASK: This allele is dominant to all others in the series and is expressed as a black mask on dogs that are not solid black. One researcher, Robinson, considers the evidence that the black mask belongs in the E series as unconvincing and assigns it to a different series.
(Ebr) - BRINDLE PATTERN: The brindle allele produces the brindle pattern with stripes or bars of dark pigment on a background of light pigment. In dogs with the dominant (As) allele, which produces a solid coat of dark pigment (brown or black), the (Ebr) allele is masked because there is no light pigment on which it can act. It is dominant over the extension (E) allele. In our breed, interactions with alleles at the B and D loci produce a rich variety of brindle colors:
Ay-B-D-Ebr- black brindle
Ay-B-ddEbr- blue brindle
Ay-bbD-Ebr- brown or chocolate brindle

Ay-bbddEbr- fawn brindle

(The (-) as the second allele at the locus pair denotes an allele that is uncertain because of the dominant nature of the first allele. It could be homozygous or heterozygous with any of the other alleles.)
(E) - EXTENSION: The E allele produces normal extension or expression of dark pigment. It interacts with Locus A alleles to produce a variety of effects:
As-E- black/brown
Ay-E- red or buckskin with or without black ticked hairs (on head and back) referred to as sable in other breeds
(ee) - RESTRICTION: The homozygous (ee) alleles restricts the expression of dark pigment, producing the yellow shades by light pigment. It does allow the expression of dark pigment on the nose, lips and eye rims. It is recessive to all other alleles in the E series. Homozygous (ee) alleles interferes with the expression of most Locus A alleles.
As-ee buckskin
Ay-ee light tan

Locus G pair: Progressive Graying
(g) uniform color throughout life
Research concludes that the AST breed are homozygous (gg) with dogs retaining their coloring throughout their lifetime. The G dominant allele present in other breeds produces a silvering or graying of the coat over time and the recessive (g) allele, giving a uniform color throughout the dogs lifetime.

Locus M Pair: Merle Pattern

(m) uniform pigment
Research has shown that our breed has only the recessive (m) allele at this locus. The homozygous recessive (mm) produces a uniform pigment in the breed. The (M) dominant allele produces the merle or dapple pattern. The dominant (M) allele has been identified in Collies, Shetland sheepdogs, Australian Shepherds, Cardigan Welsh Corgis, Great Danes, Louisiana Catalhoula, Spotted Leopard Dogs and Dachshunds.

Locus T Pair: Ticking

(t) no ticking
Research has shown that our breed has only the recessive allele (t) at this locus which in the homozygous recessive (tt) allows no ticking. The dark ticking that we see in our breed is determined on the Locus A series by the dominant (As) allele, not on the Locus T Pair. In some breeds this is known as a sable. In the APBT, traditionally this coloring is called black or brown ticked. There are modifier polygenes that control the location and extent of the black ticking in the breed. The dominant (T) allele at this locus causes the tiny flecks of pigmented hair in otherwise non pigmented (or white) areas. The T allele is typical in breeds such as the English setter and many of the hound breeds.

Locus S Series: White Pattern
The alleles of the Locus S series produce the white markings that are often seen in our breed. Researchers identify four alleles at this locus:
S solid color
si Irish spotting
sp piebald spotting
sw extreme piebald spotting
The above sequence reflects the decreasing areas of pigmented hairs. There is some question about the relative dominance of and interaction between the alleles in their heterozygous forms because the expression is complicated by modifier polygenes which affect all of the alleles. Our breed, which research shows carries all four of the alleles, show all ranges of white markings from solid colors to all white.
(S)- SOLID COLOR: The homozygous (S) alleles produce a solid colored coat. The modifiers will, on occasion, produce a small amount of white markings on the throat, chest, toes, abdomen and belly. (***KATE, INSERT DIAGRAM 1 HERE***)
(si) - IRISH SPOTTING PATTERN: This allele produces a pattern of white on the muzzle, forehead, chest, belly, feet and tail tip. The varying size of the white area is affected by the plus and minus modifiers. Breeds thought to be homozygous for this are the Boston Terrier, Basenjis and Collies. (***KATE, INSERT DIAGRAM 2 HERE***)
(sp) - PIEBALD SPOTTING PATTERN: This allele produces a widely varying areas of white. In the homozygous (spsp) genotype you would see a white dog with dark patches. (***KATE, INSERT DIAGRAM 3 HERE***)
(sw) - EXTREME PIEBALD SPOTTING PATTERN: This allele further decreases the pigmented area and, depending on the plus or minus modifiers, the pattern can range from solid white to white with spots on the ears, around the eyes, and in the tail area. (***KATE, INSERT DIAGRAM 4 HERE***)

GENOTYPE SUMMARY in the American Staffordshire Terrier:

Black As-D-E-
Blue As-ddE-
Black & Tan atatD-E-
Red AyD-E-
Fawn AyddE-
Brindle Ay-D-Ebr-
Blue Brindle Ay-B-ddEbr-
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Old 02-24-2012, 01:35 AM   #50 (permalink)
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Leigh Anne Clark *, Jacquelyn M. Wahl *, Christine A. Rees , and Keith E. Murphy *
Departments of *Pathobiology and Small Animal Clinical Sciences, College of Veterinary Medicine and Biomedical
Sciences, Texas A&M University, College Station, TX 77843

Edited by Susan R. Wessler, University of Georgia, Athens, GA, and approved November 26, 2005 (received for
review August 11, 2005)

"[Stud dog] has successfully sired four litters including three merle from a solid black Dam,
proving the solid colored Koolies can carry the merle gene and should not be culled as some
farmers have traditionaly done".

Please do not be confused about this statement, as it is not correct. A genetically solid
(non-merle) colored dog can not "carry" the merle gene.
A dog is either a merle, or it isn't.

".... we have been breeding merle to merle for 35 years, we do not produce solids .... and have
not produced any whites in over 6 years"

Unless one of their breeding dogs is a homozygous merle, they are not telling the truth.
Homozygous merles can be identified by their coloration, or better, their lack of it.
Genetic Inheritance of the Merle Gene
The merle gene (M) is inherited in an autosomal fashion. In other words, the trait is not
linked to gender and can be passed on from either the mother or the father.
The gene is incompletely dominant, or a gene that has intermediate expression. A
heterozygous dog, carrying only one copy of the merle gene (Mm), expresses the
characteristic diluted coat color pattern. A non-merle dog (mm) is normal in color, while a
homozygous double-merle (MM) is predominantly white. Punnett squares can be
used to determine the expected coat color of offspring when breeding dogs of known
genotype (i.e. coat color genes have been identified). In the example illustrated, a non-merle
dog (mm), indicated in the vertical column, bred to a heterozygous merle (Mm), indicated in
the horizontal column, will give rise to offspring with an expected frequency of 50% merle
(Mm) and 50% non-merle (mm).

Dogs that have merle gene but do not show the characteristic merle phenotype, are known
as cryptic merles. These dogs, genetically, have the merle pattern and could produce merle
offspring. It is suspected that the DNA sequence of the merle allele in the cryptic is shorter
than the allele expressed in the typical merle dog.

*Health Problems Associated with the Merle Allele
Both heterozygous merle (Mm) and homozygous double merle (MM) dogs may exhibit
auditory and ophthalmic abnormalities including mild to severe deafness, increased
intraocular pressure, ametropia, microphthalmia and colobomas. The double merle genotype
may also be associated with abnormalities of skeletal, cardiac and reproductive systems.*

Genetic Testing for the Merle Gene
with the recent discovery of the merle gene, a genetic test is now available that allows for
the identification of the merle allele. This technology is patent pending (U.S. Serial # 60/708,
589) and available exclusively thru GenMARK, the DNA technology service of VITA-TECH
Laboratories LLC. By testing dogs for this genetic trait, it is possible to:
• allow identification of merle dogs to prevent undesirable merle to merle breeding
• classify harlequin Danes as single or double merle
• identify cryptic merles
For more information, please contact Vita-Tech.
*Information obtained from GenMark
OPHTHALMIC ABNORMALITIES
Increased Intraocular pressure:
excessive pressure created in the eye.

Ametropia: vision impairment due to a
refractive error such that images fail to
focus upon the retina.

Microphthalmia: a smaller than normal
eye due to a defect occurring early in
development. Affected dogs may have
prominent third eyelids. Other eye defects
are common in animals with this condition,
including defects of the cornea, anterior
chamber, lens and retina.

Coloboma: a defect in ocular tissue; a
cleft or missing portion of components of
the eye, most commonly affecting the iris.
Coat colour in dogs: identification of the Merle locus in
the Australian shepherd breed
Benoit Hédan,1 Sébastien Corre,1 Christophe Hitte,1 Stéphane Dréano,1 Thierry Vilboux,1 Thomas Derrien,1
Bernard Denis,2 Francis Galibert,1 Marie-Dominique Galibert,1 and Catherine André1
1UMR 6061 CNRS, Génétique et Développement, Faculté de Médecine, Université de Rennes1, 35043 RENNES
Cédex, France.
25 avenue Foch 54200 Toul, France.
Corresponding author.
Benoit Hédan: benoit.hedan@univ-rennes1.fr; Sébastien Corre: sebastien.corre@univ-rennes1.fr; Christophe Hitte:
christophe.hitte@univ-rennes1.fr; Stéphane Dréano: stephane.dreano@univ-rennes1.fr; Thierry Vilboux:
thierry.vilboux@univ-rennes1.fr; Thomas Derrien: thomas.derrien@univ-rennes1.fr; Bernard Denis:
denis.brj@wanadoo.fr; Francis Galibert: francis.galibert@univ-rennes1.fr; Marie-Dominique Galibert:
marie-dominique.galibert-anne@univ-rennes1.fr; Catherine André: catherine.andre@univ-rennes1.fr
Received November 11, 2005; Accepted February 27, 2006.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License
(Creative Commons — Attribution 2.0 Generic — CC BY 2.0), which permits unrestricted use, distribution, and reproduction in any
medium, provided the original work is properly cited.
Coat colours in mammals depend on skin and hair pigment synthesis. Melanocytes
manufacture two types of melanin: the black/brown photo-protective eumelanin pigment, and
the red-yellow cytotoxic phaeomelanin pigment. Several paracrine factors secreted primarily
by surrounding keratinocytes are involved in the melanogenic pathway by stimulating the
switch between phaeomelanin and eumelanin [1]. In this pathway, microphthalmia
transcription factor (MITF) plays a central role by regulating the expression of the TYR
(Tyrosinase), TRP-1 (Tyrosine Related Protein) and DCT (Dopachrome Tautomerase)
genes that encode enzymes involved in pigment manufacture [2,3].

Coat colour is highly polymorphic in dogs. In 1957, Little described, after observing the
possible phenotypes, more than 20 loci affecting coat colours [4,5]. Until recently, only a few
genes were recognised as involved in pigmentation. However, more and more genes, alleles
and new interactions are being discovered: variants of melanocortine 1 receptor gene
(MC1R), (locus previously called extension E) [6-8], variants of Agouti, the antagonist ligand
of MC1R [9,10], variants of tyrosinase-related protein 1 (TYRP1) [11] and variants of
melanophillin [12]. Three mutations responsible for the brown coat colour versus black coat
colour were described in TYRP1 in several dog breeds including the Australian Shepherd
dog [11]. Genomic tools are now fully available in canine genetics: dense radiation hybrid
maps with 1500 polymorphic microsatellite markers and anchored BAC markers [13,14], a
radiation hybrid map comprising 10,000 canine gene-based markers [15], and a whole
sequence assembly of the canine genome, build 2.1 [16]. Altogether, the dog appears to be
a good model for understanding better the genetics of pigmentation in mammals and for
isolating new genes, new variants and interactions between alleles of different loci.

We are interested in the merle phenotype because of its involvement in coat colour and
developmental impairments. The merle phenotype is a dominant trait, with heterozygous
dogs presenting a coat colour in which eumelanic regions are incompletely and irregularly
diluted, leaving intensely pigmented patches. Merle is found throughout the body except on
the pheomelanic regions of the black and tan coat colour (Figure 1A, 1B). These dogs often
have heterochromia iridis or blue eyes and often have a lack of retinal pigment visible on the
fundus. Homozygous merle dogs display a more severe phenotype. The dogs are usually
very pale, sometimes completely white and present developmental defects with an
incomplete penetrance, microphthalmia and hearing loss (Figure 1C, 1D). In merle European
lineages, microphthalmia and/or hearing loss are not frequently observed as breeders avoid
mating merle dogs to avoid these developmental defects. However, several veterinary
studies on the "merle syndrome", reported retinal defects [17], microphthalmia and coloboma
[18]. The non-survival or degeneration of melanocytes in the cochlea have been suggested
to explain hearing loss [19].
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Old 02-24-2012, 01:45 AM   #51 (permalink)
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Retrotransposon insertion in SILV is responsible for merle patterning of the domestic dog

I can post several links and book references too since my own knowledge, research and experience can be argued.. Always is.. LOL
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Old 02-24-2012, 02:59 PM   #52 (permalink)
 
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Quote:
Originally Posted by kybully2012 View Post
Although, as for someone's statement that the merle gene is dominant and that you can have a merle pup throw a black and then that black throw is merle is inaccurate. If the merle gene is truly dominant, it will show itself over black and no other color can "hide" the merle gene. Dominant genes are never hidden. This is just a little something I've picked up from dealing with equine genetics. Hope that helped a little.
Your statement is the inaccurate one.
Dominant genes can be hidden. Ever see a yellow lab? Most labs are black (dominant) but recessive red is an epistatic gene. Since the defect it causes doesn't allow for the production of black a black dog is fawn/red, a brindle is solid, no black hairs will be on the body period.

Brindle is also considered to be dominant but clearly black will mask it and dog appears solid black. Brindle and black are at the same Locus.

Cryptic merles are merle dogs which appear solid. Merle dilutes BLACK pigment. You can have a red dog which is Mm and it still be solid red. Red, fawn, buckskin dogs can all carry merle since there is no black pigment to dilute.

When it comes to black you will almost always see the effects however some only have a small diluted patch. These are not true cryptic merle but think how this could be hidden by white in a black / white dog. You'd be none the wiser that said dog is merle until they produce.

I don't know horse genetics but I'm sure there are probably exceptions there too and at minimum clearly when it comes to dominant genes, all dominants can't express at the sametime.
As with dogs the dogs color is produced by a number of genes interacting. Red/yellow and black are dominant over their respective Loci but obviously black is dominant over yellow/red. But then you have a number of genes which can mess with black Merle causes dilution, recessive red doesn't allow it, white can "hide" any color, liver causes the coat to be chocolate, dilute causes it to be blue. Genes are always interacting.

The only thing that is true is that dominant genes will express in a heterozygous state. There is still exception to that due to incomplete dominance. Sometimes a single recessive allele has an effect and the dominant does fully express or protect against it. In some cases the recessive gene is actually a help in heterozygote but would cause harm in a homozygous state.

Merle is dominant but its fully expressed typically in homozygous animals. Double merles have further dilution / high white. Often times blind, deaf, sometimes physically deformed or non viable.

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Old 02-24-2012, 03:48 PM   #53 (permalink)
 
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Quote:
Originally Posted by KMdogs View Post
Locus A Series: Dark Pigment Pattern
This locus has six different alleles possible in the canine population. Only three are present in the APBT breed.
(As) dominant Black
(Ay) dominant Yellow
(at) bicolored pattern (tan ‘Doberman like’ markings on a solid coat)
The A alleles are pattern factors that control the amount and area distribution of dark and light pigment. They act within the hair follicle to switch pigment synthesis between light and dark. It is important to remember that alleles at this locus interact with Locus E alleles.
(As) - DOMINANT BLACK: This allele produces uniform coverage of dark pigment over the entire body. Its action is expressed in all dogs with black or brown coats. The (As) allele is almost completely dominant over others in the A series. The black color ranges from pure black to a black with a brownish cast (seal). Geneticists are uncertain if the allele is incapable to produce pure black without additional help from another locus, or if the brown cast indicates a heterozygous allele.
(Ay) - DOMINANT YELLOW: The (Ay) allele restricts dark pigment, producing yellow colors. When homozygous, the coat can be clear gold, but often has black tipped hairs, especially on the head and down the back.
(at) - BLACK AND TAN PATTERN (BICOLORED): The typical tan points are above each eye, on each cheek, on the lips and lower jaw, extending under the throat, two spots on the chest, below the tail, and on the feet to the pasterns and hocks, extending up the inner sides of the legs. These tan points can occur on black or seal, blue, chocolate or red solid colored dogs. A great deal of variation can occur with these tan points, even within the depth of the pigment. In some dogs the tan points are not always marked and the color contrast is not always distinct.

Locus B Series - Black/Brown Pigment
(B) black pigment
(b) brown pigment
This locus contains only two alleles, the dominant (B) producing black skin and nose pigment and the (b) recessive allele, producing brown pigment. In dogs that are red or buckskin, the Locus (B) alleles are expressed in skin color, most visible around the eyes and nose. The black nose indicates the genotype is (BB) or (Bb), both which would be expressed as black nose because of the dominance of the (B) allele. A light brown or red nose is (bb), or homozygous recessive. Being homozygous recessive, both parents must contribute one recessive (b) gene to the offspring to produce the red nose. When breeding two dogs with the (bb) genotype, the only resulting combination in the pups would be ( bb) or red nose.

Locus C: Pigment depth
The Locus C series controls the production of pigment throughout the coat. In dogs, the expression of the Locus C alleles is based on observation rather than experimental studies. The American Staffordshire Terrier breed is felt to have only the dominant (C) allele at this locus. The C allele allows the full expression of color, of dark and light pigments. The allele (cch) or Chinchilla Dilution, found in other breeds at this locus, causes the light pigments to be diluted out in various degrees. This would account for the varying shades found in many littermates depending on their homozygous or heterozygous pairing. The chinchilla dilution allele (cch) does not affect the dark pigment, thus allowing for the white dog with black skin pigment and black nose. Other researchers (Robinson) feel that other modifier polygenes are responsible for this phenotype.
CC full color
Ccch medium shade
cchcch pale shade

Locus D pair: Pigment density
(D) intense pigment density
(d) dilute pigment density
The locus D pair modifies the density of the pigment. The dominant (D) gives full density in both the heterozygous (Dd) or the homozygous (DD) combination. The homozygous recessive (dd) alleles dilute the color. When the dogs basic color is produced by dark pigment, genotype (Bbdd) or (BBdd) yields the color known as blue. The black coat is modified as well as the skin pigment to a gray or blue pigment around the eyes, pads and nose. When the dogs basic color is produced by a light pigment the genotype bbdd (dilute brown pigment) produces a fawn with a silvery cast known in our breed as a fawn/bluies. The skin pigment around the eyes is flesh colored as well as a red or brown colored nose.

Locus E Series: Extension
(Em) black mask
(Ebr) brindle

(E) extension of dark pigment

(f) restriction of dark pigment
The Locus E alleles affect the extension of dark pigment, and all of the alleles at this locus interact with those of locus A.
(Em) - BLACK MASK: This allele is dominant to all others in the series and is expressed as a black mask on dogs that are not solid black. One researcher, Robinson, considers the evidence that the black mask belongs in the E series as unconvincing and assigns it to a different series.
(Ebr) - BRINDLE PATTERN: The brindle allele produces the brindle pattern with stripes or bars of dark pigment on a background of light pigment. In dogs with the dominant (As) allele, which produces a solid coat of dark pigment (brown or black), the (Ebr) allele is masked because there is no light pigment on which it can act. It is dominant over the extension (E) allele. In our breed, interactions with alleles at the B and D loci produce a rich variety of brindle colors:
Ay-B-D-Ebr- black brindle
Ay-B-ddEbr- blue brindle
Ay-bbD-Ebr- brown or chocolate brindle

Ay-bbddEbr- fawn brindle

(The (-) as the second allele at the locus pair denotes an allele that is uncertain because of the dominant nature of the first allele. It could be homozygous or heterozygous with any of the other alleles.)
(E) - EXTENSION: The E allele produces normal extension or expression of dark pigment. It interacts with Locus A alleles to produce a variety of effects:
As-E- black/brown
Ay-E- red or buckskin with or without black ticked hairs (on head and back) referred to as sable in other breeds
(ee) - RESTRICTION: The homozygous (ee) alleles restricts the expression of dark pigment, producing the yellow shades by light pigment. It does allow the expression of dark pigment on the nose, lips and eye rims. It is recessive to all other alleles in the E series. Homozygous (ee) alleles interferes with the expression of most Locus A alleles.
As-ee buckskin
Ay-ee light tan

Locus G pair: Progressive Graying
(g) uniform color throughout life
Research concludes that the AST breed are homozygous (gg) with dogs retaining their coloring throughout their lifetime. The G dominant allele present in other breeds produces a silvering or graying of the coat over time and the recessive (g) allele, giving a uniform color throughout the dogs lifetime.

Locus M Pair: Merle Pattern

(m) uniform pigment
Research has shown that our breed has only the recessive (m) allele at this locus. The homozygous recessive (mm) produces a uniform pigment in the breed. The (M) dominant allele produces the merle or dapple pattern. The dominant (M) allele has been identified in Collies, Shetland sheepdogs, Australian Shepherds, Cardigan Welsh Corgis, Great Danes, Louisiana Catalhoula, Spotted Leopard Dogs and Dachshunds.

Locus T Pair: Ticking

(t) no ticking
Research has shown that our breed has only the recessive allele (t) at this locus which in the homozygous recessive (tt) allows no ticking. The dark ticking that we see in our breed is determined on the Locus A series by the dominant (As) allele, not on the Locus T Pair. In some breeds this is known as a sable. In the APBT, traditionally this coloring is called black or brown ticked. There are modifier polygenes that control the location and extent of the black ticking in the breed. The dominant (T) allele at this locus causes the tiny flecks of pigmented hair in otherwise non pigmented (or white) areas. The T allele is typical in breeds such as the English setter and many of the hound breeds.

Locus S Series: White Pattern
The alleles of the Locus S series produce the white markings that are often seen in our breed. Researchers identify four alleles at this locus:
S solid color
si Irish spotting
sp piebald spotting
sw extreme piebald spotting
The above sequence reflects the decreasing areas of pigmented hairs. There is some question about the relative dominance of and interaction between the alleles in their heterozygous forms because the expression is complicated by modifier polygenes which affect all of the alleles. Our breed, which research shows carries all four of the alleles, show all ranges of white markings from solid colors to all white.
(S)- SOLID COLOR: The homozygous (S) alleles produce a solid colored coat. The modifiers will, on occasion, produce a small amount of white markings on the throat, chest, toes, abdomen and belly. (***KATE, INSERT DIAGRAM 1 HERE***)
(si) - IRISH SPOTTING PATTERN: This allele produces a pattern of white on the muzzle, forehead, chest, belly, feet and tail tip. The varying size of the white area is affected by the plus and minus modifiers. Breeds thought to be homozygous for this are the Boston Terrier, Basenjis and Collies. (***KATE, INSERT DIAGRAM 2 HERE***)
(sp) - PIEBALD SPOTTING PATTERN: This allele produces a widely varying areas of white. In the homozygous (spsp) genotype you would see a white dog with dark patches. (***KATE, INSERT DIAGRAM 3 HERE***)
(sw) - EXTREME PIEBALD SPOTTING PATTERN: This allele further decreases the pigmented area and, depending on the plus or minus modifiers, the pattern can range from solid white to white with spots on the ears, around the eyes, and in the tail area. (***KATE, INSERT DIAGRAM 4 HERE***)

GENOTYPE SUMMARY in the American Staffordshire Terrier:

Black As-D-E-
Blue As-ddE-
Black & Tan atatD-E-
Red AyD-E-
Fawn AyddE-
Brindle Ay-D-Ebr-
Blue Brindle Ay-B-ddEbr-
Guess I type slow lol. 3 post or so before I finished my one
If we are going to educate people shouldn't we do it with UTD and accurate information? I think so.

I was shocked they said truly dominant means it can't be hidden. They are wrong, wrong, wrong.

But the post which I've quoted list dominant black at A Locus, RECESSIVE black is at A Locus (which doesn't appear likely to be in APBT, its in a few breeds only. Though I'm not saying its impossible as in some breeds certain recessive showed an extremely low allele frequency and no homozygous dogs were found, but could occur.) Dominant black is at K Locus as is brindle (quoted post states E Locus).
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