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The Genetics of Breed Color In The American Pit Bull Terrier


by Amy Greenwood Burford 

 

     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

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