Color in the BT - The Layered Approach or..
"Where did that RED one come from?”-
Kevin Welch ©1988
The variation of colors in a litter of Bull Terriers can be quite surprising and seem totally unexplainable when neither
parent is of the same color as the offspring. Traditional explanations are usually offered in technical genetic terms which
may be the 'meat and potatoes' for scientists but only put off those of us looking for a practical understanding for our
breeding programs. Now, Fess up, do you really want to hear about alleles or heterozygotes? I thought not.
Several years ago I read an article in Mackay-Smith's "From James to Jim" which used a layered model to examine
color in the BT. We will extend this interesting approach to all aspects of color in the breed and, hopefully, provide a fairly
accurate framework for understanding this complex genetic process.
While we don't know as much about color as we'd like, there are a few things which seem certain:
1) White to white always yields white.
2) Brindle must exist in at least 1 parent to yield brindle
3) Brindling always expresses itself (Dominant).
Thus, if you lose brindle (and you can) you must regain it elsewhere. This is the reason for "...other things being
equal, brindle is preferred." Once lost in the breed, brindle would be gone forever. Therefore, it is important that we
attend to matters of color and learn as much as we can about it.
THE LAYERED MODEL
Look at your Bull Terrier and realize that whatever color s/he seems, s/he is really Red or Fawn (which may be nothing
more than a dilution of red). And that what you see is really only what shows through after your Red/Fawn dog has received 3
more coats of genetic paint. To repeat, all BI's are Red/Fawn with 3 more layers of color on top. Each layer is genetically
programmed and may (or may not) be visible depending on characteristics of any upper layers. We shall start with the lowest
layer, just above the base color of red/fawn.
I . T h e M A R K I N G S L a y e r
The Markings layer has 3 possibilities: Brindle, Smut (mask), or Clear (in that order). Brindling is a striped pattern
which permits the underlying red/fawn to show through but it also may be so tight a pattern as to appear almost solid
black. Smut appears as a black mask around the muzzle and shows only in the absence of brindle. This layer may also be
Clear (neither brindle nor smut). The BT with a clear Markings Layer cannot pass on either brindle or smut.
II. The BLACK Layer
The BLACK Layer overlays the red/fawn base and the MARKINGS Layer. It shows as either on or off. Where 'on', it
acts as a black coat from the head to the tail, down over the back and sides of the body, and 1/2 way down the front of the
legs. It is the action of this layer which differentiates the Black-brindle from other Brindles. This layer may also be clear
(appears "off'). (Since red-to-red matings appear to produce BLACK Layer action in 25% of pups, the Black Layer would
seem to act recessively).
III. The WHITE Layer
The WHITE Layer is the uppermost of the 3 layers and appears to express itself in 3 ways:
Total
White, Irish
Spotting, and Clear. As the topmost layer, it overrides the visible effects of the lower layers. Therefore in the case of Total
White, unless there are breaks in the cover (such as eye patches, etc.) the status of each independent lower layer is
uncertain. Irish Spotting is the name given to the pattern of white collar, blaze, chest, feet and occasional tail-tip. Some
animals would appear to be clear, or nearly clear, at the WHITE Layer. These are the solids and are not known to yield
white offspring (affirming that Total White acts recessively).
BTCNE Newsletter 4
