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

This model is able to describe the dog we see and, yes, would seem to explain 'where that RED one

came from' (because they are ALL red!). But from the standpoint of "What can I expect from breeding
my bitch to THAT dog?", the model alone falls short. That's basically because every dog has 2 parents
and each layer is activated by the combined effect of 2 signals (1 from each parent) with the stronger
signal winning out. Remember though, when it is bred, the dog will transmit BOTH signals to its litter

with each pup picking up just 1 of those 2 signals from each parent.

For example, your brindle dog might be 'pure' for brindle (2 brindle signals in the MARKINGS Layer)

OR the same dog might actually have 1 brindle signal and 1 smut signal (you’ll still see only brindle). When
bred to a Red & White with a clear MARKINGS Layer, the "pure" brindle will activate the MARKINGS
Layer of all pups with brindle. But if instead s/he "carries smut" along with that brindle signal (1-BR, 1-
SM), then only 50% of the pups will get the brindle and the other 50% will carry smut. The brindle-
activated pups may show as Total White, Black-brindle, or Brindle while the others may be Total White,
Red Smut, Fawn Smut, Tri, B&W or even Black & Tan - depending upon the other layers. It is because
there are 2 signals in this MARKINGS Layer of each parent that brindle-to-brindle matings lead to brindle
pups in only 75% of the cases.

Thus, in order to really predict within a margin of error what colors we'll get from a particular mating

with a colored BT we must have 1) a good understanding of the action of each factor in the 3 layers, 2)
knowledge of the mates, their color background, and progeny, and perhaps most importantly 3) a large

enough litter for chance probabilities to occur.

Base Markings Black Layer White Layer

Layer

F

awn

BTCNE Newsletter 2

Color cont'd
The following table shows the color distribution of over 2000 Bull Terriers and the color of the parents.

The raw data was obtained by Briggs and Kaliss (1942) from

a

survey of Bull Terrier breeders of the time.

Along with those shown numerous animals were not included because the records of these dogs left some

uncertainty as to their color or that of the parents. It is interesting to note that the literature also referred to

a single

blue

Bull Terrier. I re-tabulated the data to show the probability of color outcomes from color

matings. Where the last column is low, it indicates that the data records very few matings of this color

combination. As a result, color distribution for those combinations may be over- or under-stated and any

conclusions drawn from these pairings should be considered tentative.

Color Distribution: Frequencies and Percentages for the Major

Color Combinations

BTCNE Newsletter 3