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.