GENE SERIES AND ALLELES AFFECTING COAT COLOR IN DOGS, by Lisa Harper

In our breed it is often said, "The color of the Spanish Water Dog is magic!" Indeed, we enjoy a wide variety of colors, shades, and white patches in our breed. But other than the hidden surprises issued by recessive genes, coat color in dogs can generally be explained through color studies conducted in the mid-20^th century.

Before we start, let’s get some basic terms under our belts. The phenotype is what you see, as compared to the genotype—the genes the dog actually carries. Coat color is polygenic, meaning more than one gene series are involved. At least eleven gene series have been identified to impact coat color in dogs, all of which have at least two alleles (variations). The alleles of each gene series can be ranked by dominance. A dog inherits one gene from each gene series from each of his parents. The most dominant genes are the ones expressed (phenotype). However his genotype contains both the dominant and recessive, and he could pass either onto his offspring.

The most easily understood color series is the "B" series, which dictates whether a dog is genetically black or genetically brown. In a breed with a wide variety of colors such as the Spanish Water Dog, genetically-black and –brown dogs may be confused since black dogs with color-modifier genes may actually appear to have brown, beige, or white coats! The true test of whether a dog is black or brown is the color of its nose. If the dog has a black nose, it is a genetically black dog no matter what color the coat, and the dog may produce black-coated puppies. A brown nose indicates a genetically brown dog who only carries the recessive brown gene (no black) and must be mated to a a dog carrying black (B) to produce black puppies.

Let’s look at how a mated pair of dogs passes on the "B" series to its offspring. For this example, let’s say each parent is homozygous (has two of the same alleles). One is black (BB), and one is brown (bb). Remember, each parent passes on only one of it’s two genes to each offspring! In these types of diagrams, one parent is represented on the top line, and the other down the left side.

In this example, all of the offspring produced are heterozygous (have more than one allele) with a code of Bb. Since B (black) is dominant to b (brown), all of these pups’ phenotypes (expressed appearance) are black, but they all carry the code for brown. If we were to mate two of these heterozygous pups together, we would see this:

Statistically, 25% of the pups will be homozygous black (BB), unable to produce anything but phenotypically black pups. 50% will be heterozygous black (Bb), able to produce both black and brown pups (providing the mate carries brown). 25% will be homozygous brown (bb).

The gene series presented here are those thus far determined in dogs as a whole. Individual breeds may or may not carry certain alleles. Some breeds such as the Norwegian Elkhound are almost entirely homozygous in all the gene series, meaning the coat colors are more or less the same for every dog in that breed. Others, like the Spanish Water Dog, enjoy a much wider variety of alleles in each series, thus exhibiting a wide range of coat colors. The alleles present in Spanish Water Dogs are addressed towards the end of this article.

This series controls the distribution of dark color in the overall coat of the dog.

This series determines whether the dog is genetically black or brown. To tell which a dog is, look at the nose color. While the coat color can be effected by the other gene series, the nose color is always determined by the B series.

The B series also has some effect on the color of the eye (iris). Generally, B- produces a darker eye color than bb. Yellow eyes (sometimes called "headlights") are attributable to the D Series.

The C series is sometimes called the "chinchilla" or "paling" gene, controlling the amount of pigment deposited in each hair shaft. Yellow and red shades are effected first. Dark is only effected by the most extreme alleles. The C series is what causes the color white in Poodles and probably in Spanish Water Dogs. The C series also carries two (uncommon) alleles for albino.

This gene series is often referred to as the dilution series and is comprised of only two alleles. In many breeds, dilution is only expressed in brown dogs.

Many geneticists assert that yellow eyes ("headlights") are an expression of dd, although I suspect that the trait is polygenic.

This gene series controls the extension (or pattern) of dark color in the coat. In horses, it has been shown that ee allows black pigment in the skin, but not in the hair. This is similar in breeds such as the Poodle, where ee restricts black and liver to the nose and eyes and only allows slight shades of red-yellow.

Hypothesized by only a handful of more recent color geneticists, the flecking of white hairs throughout a dark coat might be controlled by the F series.

This hypothesis would seem to apply more to breeds such as the Australian Cattle Dog than to water dogs. In most water dog breeds (Portuguese, Spanish, Romangalo, Poodle, etc.), white hairs almost always appear in the adult coat.

This series determines the progressive silvering of a coat. In Poodles, for example, some dogs born dark silver as they mature. This is in contrast to the P series, whereby a dog may be born silver and remain silver.

The M series is also known as the Merle gene series. Merling is often seen in the collie breeds, where irregular darker blotches appear on distinctly lighter backgrounds of the same color.

M seems to be a "minus modifying gene". (s^i,, s^p, s^w) are inclined to have more white spotting. Solid dogs (S-) may not show increased spotting.

The M series also also has several other effects, including effect on eye color (partially or wholly blue iris), albinism (in combination with c^b or c^a), and some birth defects.

The P series seems to determine the depth of dark pigment in the coat from birth. Remember the G series? A bbG- dog born dark brown will mature into a silvery brown adult. A bbpp pup may be born that same silvery brown color, yet its genetic code is completely different than the first pup.

The S series dictates the amount of white spotting in the coat. Often, we will say a dog is white with colored patches. In reality, it is a colored dog with very large white patches!

Some breeders waste a lot of effort trying to breed pure white dogs from parti or extreme piebald stock. While this method of breeding will increase the size of white patches, some dark will always appear somewhere on the body. True white dogs are S- (solid color) with extreme color modifiers in the other gene series.

As a note of caution, skin under white patches is generally pink from lack of pigment and is subject to sunburn.

The T series controls the appearance of dark hairs ticked throughout a white coat.

The Poodle information below primarily comes from The Inheritance of Coat Color in Dogs by Clarence C. Little, published 1957 by Howell Book House. The Spanish Water Dog and Portuguese Water Dog information is from my own notes, as neither breed was on the U.S. radar in the 1950's.

While the alleles available in all three breeds are primarily the same, note the differences in the "A", "C", and "S" series. Multiplied by the number of possible combinations, there are a lot of possibilities available!

Although the Spanish Water Dog breed has existed for centuries, only recently have generations been bred according to a written standard. Although disqualified for the show ring and breeding, some Spanish Water Dogs lines carry colors or patterns not allowed by the current standard. Some of these are dominant traits (i.e. ticking [T]) or recessive (i.e. tri-colors or tan point [a^t]). The dominant traits are, naturally, easier to breed out: any dog carrying the trait will exhibit it. However, the recessive traits will continue to pop up unexpectedly for many generations.

In order to track color genetics in our breed, we must establish a few guidelines.

1. Refer to the color of a dog by the color of its nose in addition to coat color. For example, "a beige dog with a black nose" would tell us the dog is genetically black and may produce black puppies!
2. Standardize names of colors. Is light yellow-y brown to be called beige, sand, or buff?
3. Devise a way to discern the dogs that are born one color and mature into another from the dogs that are born that second color. Genetically, there is a big difference between a parti-colored pup with very light brown patches on its ears that fade to white by maturity, compared to a dog born pure white. Two such dogs bred together would probably NOT produce white puppies!

WHY NOT TO BREED FOR COLOR

It can be very tempting to breed for a line consistent in a flashy color or pattern, and fairly easy to do, especially if the pattern or color you like is recessive: simply eliminate all of the more dominant colors or patterns from your gene pool. However, this is a fast path to disaster.

One of the crucial elements to keeping a gene pool strong is through continuing diversity.

For simplicity's sake, let's say a breeder is partial to brown and wants a purely brown line. In the first litter of eight, two pups are born brown and six are black. The breeder retains the brown pups for his breeding line and pets-out the blacks. Short-term, the breeder has a sure-path to achieving a brown line, but he has thrown out 75% of his line's genetic diversity to do so!

Ask yourself: what is most important? A cosmetic element, or the long-term health of your line?