Molecular Genetics of Norwich Coat Color

The Molecular Genetics of Norwich Coat Color

The study of the genetics of canine coat color predates molecular genetics (using DNA to understand genetics). Not everything is known about coat color, so this is still an active area of scientific research. Here I present my understanding of the molecular genetics of Norwich terrier coat color. My understanding is based upon my reading of the literature on the subject, my own observations, and DNA testing of approximately 300 Norwich terriers. This is still a topic about which I am learning; if anyone has more information on the subject I would be happy to hear about it.

The genes that control canine coat color were historically called the A-Locus, B-Locus, D-Locus, E-Locus, K-Locus, etc. If you do a DNA coat color panel test on your dog, the results likely will be reported using these historical names.

For Norwich terriers the only ones of interest are the A-Locus, the E-Locus, and the D-Locus. For all the others, molecular genetics has shown that they are "fixed" in Norwich ... meaning that their values are all uniformly the same for all Norwich; thus they do not affect the different coat colors we see in Norwich terriers.

A-Locus

There are two alleles (variants), ay and at, of the A-Locus. If a Norwich is an ay/ay at the A-Locus, then the dog will be a red ... with possibly some black on the face, tips of the ears, and tail (see the E-Locus for more information). If a Norwich is an ay/at, then the dog will either be a red or a grizzle. A relatively new DNA test - available from UC-Davis - now can distinguish between red and grizzle. (See below.) If the dog is a at/at, then the Norwich will be a "black-and-tan".

On the Norwich that I have DNA tested, the distribution is

ay/ay = 22 percent (red)
ay/at = 51 percent (red or grizzle)
at/at = 27 percent (black-and-tan)

The individual allele distribution is

ay = 48 percent
at = 53 percent

Grizzle

UC-Davis now offers a more complete breakdown of the A-Locus, with three variants appearing in Norwich. The ay variant can either be dy (dominant yellow) or sy (shaded yellow). UC-Davis renames the at allele as bs (black saddle). Here is the relationship of the coat colors and the variants.

Coat color UC-Davis Traditional
red
dy/dy
ay/ay
dy/bs
ay/at
dy/sy
ay/ay
sy/sy
ay/ay
grizzle
sy/bs
ay/at
black and tan
bs/bs
at/at

E-Locus

For Norwich, there are three alleles (variants): Em, E, and e. (This is the area where my understanding is weakest.) If a Norwich has the Em allele, then it will have some black on the face, tips of the ears and tail. If a Norwich is an "ee" then it will be a "pinkie" - at birth its pads and nose will be pink, but within a few days will darken. An "ee" dog will have no black hairs on its body.

On the Norwich that I have DNA tested, the distribution of the E-Locus is

Em = 39 percent
E = 53 percent
e = 9 percent

D-Locus

There are two alleles (variants), D and d, of the D-Locus. Most Norwich carry the D allele. If an otherwise black-and-tan Norwich (atat) is dd on the D-Locus, then it will be a "blue-and-tan". An otherwise red Norwich who is dd will have a really strong wheaten color, almost white. A dog has to carry two copies of the d allele to cause these "dilution" effects. The "d" allele has been associated with "color-induced" hair loss (alopecia)

Of the Norwich that I have DNA tested, the distribution of the D-Locus is

D = 97 percent
d = 3 percent

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