Further explanation is warranted about the coloration's seen in today's Rat Terrier, how they were developed and how Mendilian's Law (the law of odds) allowed them to naturally occur.  To understand coloration in dogs one must first keep in mind three things because they will dictate what occurs in a litter:

1. Dominant Color Gene - a gene if present that will always show to the naked eye.
2. Recessive Color Gene - a gene that requires both parents to carry it in order to visibly show up on the dog.
3. Mendilian - the ratio of colors or traits that will be produced when you combine certain color genes.
Listed below is a chart showing color genes from each series that are carried in the Rat Terrier and their order of dominance. Those listed in capitol letters are dominant.

Most Dominant

Least Dominant
. ..

     Each dog carries (Two) genes from each of the Ten series listed above in any combination. Example: AAy, Bb, CC, Dd, Eebr, gg, mm, PP, Ssp,tt. They pass one of each gene along to their offspring. Of those listed above  we will refer to the genes having the most impact on the colors we will talk about. Beside each gene is a description of the color or part of the color that these genes affect.

A=black, red, yellow B=black nose C=full pigmentation D=no dilution Em=mask S=solid no white
ay=sable,tan,fawn b=chocolate Cch=extreme dilution d=dilution E=full pigmentation si=irish spotting
at=black and tan . . . ebr=brindle sp=piebald
. . . . e=restricts color sw=extreme white
     There was a predominance of Black, white and tan (Tri), that came from the Smooth Fox and Toy Fox Terrier. The Black and tan (Bi) color can easily be explained by the Manchester Terrier. Provided the black and tan Manchester color is true, and only carries the (S) gene that does not allow white in the coat, this dog bred with the Tri color dog, will produce all black and tan puppies. The (S) gene for (no white) is dominant over any of the other (S) genes that the Tri may carry.

     The introduction of the Whippet, Italian Greyhound, Greyhound and Chihuahua breeds that came in many different colors (red, brindle, liver, chocolate, black, white, fawn, sable, lemon, blue, apricot and cream) dispersed the Rat Terrier population with all of them. Some of these colors, carry the (A or ay) gene in double dose which makes them dominant over black and tan (at). When you breed the (A) or (ay) genes with (S) you can produce any solid color except solid white. In other words, if you breed a black and tan (atS) (Manchester) dog to a black and white dog (A sp/si), all of the offspring will be solid black. The (S) gene which does not allow white will clearly show itself so there will be no mistaking that the dog carries it [making it easy to control.]

     The Rat also comes in a large variety of patterns. Sometimes with spots or patches (blankets) of color with or with out tan markings and all solid colors. There is color on the head of most Rat Terriers unless it carries the (sw) gene in double dose in which case it will be solid white in most instances. It is a recessive gene and hides behind all colors when seen in single dose.

Solids, Tri's, and Bi's in their truest form have these gene makeup's:

White - AA or ayay or atatBBCCDDEEswsw
Clear Red & Lemon - AABBDDeeSS
Tan, Fawn, Red - ayayBBDDEESS
Sable - ayatBBDDEESS
Tri Black, White and Tan - atatBBDDEEspsp or sisi
Bi Black and Tan - atatBBDDEESS
Bi Black and White - AABBDDEEspsp or sisi

     Colors such as Blue, Tan Apricot, Charcoal, Weimaraner Gray/Pearl, and Cream are classified as dilute colors. Many  Rat Terriers that appear to be Tri, Bi, or solid colored carry these colors. In order to produce them, both parents must carry the particular color in their background or actually be these colors. Their truest gene makeup's are:

Blue (grey) - AA or atatBBddEESS or spsp or sisi
Tan Apricot  - AA or ayayBBddEEGGSS or spsp or sisi
Charcoal - AABBCCddEESS or spsp or sisi
Weimaraner/Pearl - AAbbCCddEESS or spsp or sisi
Cream - AA or ayay or atatBBcchcchDDeeSS or spsp or sisi

     The color chocolate or liver is another gene that must be in both parents' background or the offspring will not be this color. It is the action of the (bb) gene that turns the black dog to a chocolate or liver color. The
distinguishing factor in these dogs is that their nose is also the same color as their coat and never black.
Chocolate - AA or atatbbCCDDEESS or spsp or sisi

     Please note that there are other combinations that can produce the same colors that we have listed above.
     Now that we've seen what makes up some of the dogs lets do a sample Mendilian cross, keeping in mind that each puppy inherits one of each gene from each series from each parent.

     If you cross a Chocolate dog with the formula AatbbCCDdEESsp to a Black and White dog with the formula AatBbCCDdEEsisp all of the following colors can be produced:
(Black & White)- (Blue & White)- (Chocolate & White)-(Weimaraner Gray/Pearl & White)-( Tri Black)-(Tri Blue)-(Tri Chocolate) -(Tri Silver)-(Solid Black)-(Solid Blue)-(Solid Chocolate)- (Solid Weimaraner Gray/Pearl)- (Black & Tan)-(Blue & Tan)- (Chocolate & Tan) - (Weimaraner Gray/Pearl & Tan)

     The colors that you get are dependent upon litter size and how many time's gene combinations can be repeated. The following inherited combinations of genes produce these colors:
     (Remember that those genes listed in capitol letters are dominant and that Two recessive genes (small letters) must come together to be seen visibly on the coat)

Black & White = AA or AatbBCCDd or DDEEspsi or spsp 
Blue & White = AA or atAbBCCddEEspsi or spsp 
Chocolate & White =AA or AatbbCCDd or DDEEspsi orspsp 
Weimaraner Gray/Pearl & White = AA or AatbbCCddEEspsi or spsp 
Tri Black = atatbBCCDD or dDEEspsp or spsi 
Tri blue = atatbBCCddEEspsi or spsp 
Tri Chocolate = atatbbCCDd or DDEEspsp or spsi 
Tri Weimaraner Gray/Pearl = atatbbCCddEEsisp or spsp 
Solid Black = AA or AatBbCCDd or DDEESsp or Ssi 
Solid Blue = AA or AatBbCCddEESsp or Ssi 
Solid Chocolate = AA or AatbbCCDd or DDEESsp or Ssi 
Solid Weimaraner Gray/Pearl = AA or AatbbCCddEESsi or Ssp 
Black & Tan = atatBbCCDD or DdEESsi or Ssp 
Blue & Tan = atatBbCCddEESsi or Ssp 
Chocolate & Tan = atatbbCCDD or DdEESsi or Ssp 
Weimaraner Gray/Pearl & Tan = atatbbCCddEESsi or Ssp
     The reason for all these colors is in how the genes combine, (AA) produces black color when combined with (DD or BB), when it combines with (bb) you get a chocolate color, (AA) combined with (dd) will make the color blue. (atat) which produces the tan markings combined with (si or sp) will give you a Tri colored dog. If it also carries the (dd) gene it will be a Tri blue and if it carries the (bb) gene it will be a Tri Chocolate color. When the (Aat) gene are seen together along with the (DD or BB) the (A) dominates the (at) gene and therefore produces the color black and does not let the tan color come through. And so if the dog carries the (bb or dd) gene the dog will be chocolate or blue respectively but will not have the tan markings. The (si) gene in combination with any of the above will allow markings of white to appear (chest, blaze, boots, collar). When the (sp) gene appears with any of the above combinations the dog will show markings of piebald or patches of color. The (S) gene allows some of the pups to be a solid color.

     We knew which genes the above dogs were carrying by knowing the color lineage behind them. It is of great value to at least know what color the parents were. In the case of your dog being a certain color, example chocolate or blue, the color itself tells you which genes the dog is carrying. Many times it is hard to determine what genes your dog may be carrying if they are recessive in nature. Recessive genes can be carried and hidden for many generations and only become visible when bred to a dog carrying the same recessive gene.

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