“The Myth of The Pattern White”
Pattern Whites in Non-Merle to Merle Breeding
The Pattern White Australian Shepherd is distinctly different from the white Double Merle Aussie. Although many have confused the two because of predominantly white body color or white body splashes, in actuality their coat color is inherited through entirely different genetics.
Let me explain. Genetic theory tells us that each cell is comprised of two chromosomes, one contributed from each parent. Each chromosome is comprised of genes, which are the basic units of inheritance. Genes are arranged in a linear order on chromosomes. On these chromosomes are specific locations called loci (singular: locus) where genes, or more specifically gene pairs, are located. The various forms of a gene that can be located at the same site (locus) are called alleles. In dogs, ten loci have been identified which contribute to coat color: A,B,C,D,E,G,M,P,S and T. Some of these loci may contain any one of several alleles (called multiple alleles), some only two. The various alleles that make up gene pairs on the chromosomes are the genetic make-up of the individual. This is called the genotype. In contrast, how we actually see these alleles expressed in the individual (i.e., coat color, eye color) is called the phenotype.
In dogs, the “B’ locus is the major determinant of body color. The (B) allele is dominant and produces black body color. The (b) allele is recessive and produces a red or liver color. These are the two body colors recognized by our breed standard. However, Aussies have been blessed with an unusual coat color variation of both the above body colors called the merle. This merling pattern is also found in many herding breeds like Collies, Shelties and Border Collies.
The “M” locus is the site of the merle alleles, which produce the merle coat color pattern. This locus contains two alleles: The (M) allele is dominant and produces the merling pattern and the (m) allele is recessive and produces uniform pigmentation, or predominantly solid body color (black or red). Healthy merles (a misnomer) are genetically Mm – which means heterozygous. Applying genetic theory, when breeding two merles together, Mm x Mm, the results of the breeding will statistically produce 25% solid dogs (mm, homozygous), 50% healthy merle dogs (Mm, heterozygous) and 25% double merle (MM, homozygous). It is this double dominant combination that can also carry what some have referred to as “lethal white” genes, (although this term is actually a misnomer) causing deafness, blindness and some even say heart problems. Typically, double merles puppies can have excessive white body color, little or no color around the eyes and ears and may be deaf or blind. The propensity for deafness and blindness has been found to be genetically linked to coat color however deafness and blindness may – or may not – occur. Some double merles live perfectly healthy lives, some with more body color than others. In fact, some breeders like to keep double merles in their lines as they will always produce merle puppies, whether bred to solids or merles.
The Pattern White is not a Double Merle in any way. Since one or both of its parents are solid, the Pattern White is genotypically (the dog’s genetic make-up) either BB, Bb, or bb having either predominantly black (BB or Bb) or red/liver (bb) body color. At the “M” locus, this individual would be Mm or mm. This dog may have tan markings or “tan points” (contributed from the “A” locus) or a varying distribution of white marking. It is the “S” locus which effects the distribution of white coloring over the body’s surface. In contrast to the “M” locus, the “S” locus has four alleles: S, Si, Sp and Sw. These alleles effect body color in the following ways: (S) – completely pigmented body surface (solid), (Si) – typically called the Irish Spotting Pattern with white patterns occurring in specific areas (i.e., collie collar, white blaze, white socks), (Sp) – the Pattern White or, more correctly the Piebald, with usually white body coloring with a solid saddle pattern, typically seen in Beagles, and (Sw) – extreme white or albinoism. These alleles may have plus and minus modifiers which can either increase or decrease the allele’s effect, as well. Minus modifiers produce more white while plus modifiers reduce white.
The Pattern White (also called Piebald) is a product of the influences of the “S” alleles and not the merling gene (M). Although this dog is genotypically a solid dog, it is the “S” alleles which determine how much white is distributed over the body’s surface. Since Aussie genetics are often still misunderstood, looking at the genetics of its close relative, the Collie, is very informative. The Collie has the same operative alleles as the Aussie. Based on Collie genetics, it is unclear whether the Pattern White is truly a pattern (SiSi) or a Piebald (SpSp) or both (SiSp) or, as Little (Clarence Little, The Inheritance of Coat Color in Dogs, Howell Books, 1957) offers, there may be incomplete dominance of Si over Sw, as well. Since plus and minus modifiers may act upon all the “S” alleles, this makes precise identification very difficult without specific DNA testing or test breeding. Nonetheless, existing literature suggests that what we refer to in our breed as the Pattern White is produced by the “Sp” piebald allele since the Irish Spotting Pattern “Si” allele is more specific to certain body areas and “Sw” is closer to extreme albinoism.
My Freya (Freya Delamere ATDs OTDc STDd CD CGC TDI Therapy Dog) was an excellent example of a Pattern White Aussie. Freya’s sire was a red-bi and her dam was a black tri. Genotypically she was a black tri (BB or Bb), however the influence of her “S” alleles contributed to excessive white marking, giving her the appearance of white body color. Freya also had a ticking pattern in her coat color (influenced by the “T” locus.) It is this phenotype (what she looked like), excessive white with ticking, that is often confused with the Double Merle to those who don’t understand coat color genetics. However, the ticking pattern cannot be merling as we know definitively that neither of her parents were merles: she was (mm) at the “M” locus. Freya came from very old Northern California/Oregon lines which often produced pattern whites. Talking with knowledgeable old-time breeders from this region suggests that the “S” alleles that produced this color pattern act as simple recessives. In other words, only when two dogs were bred that carried this “S” allele recessive, did the breeding produce pattern white puppies. What we know of Freya’s lines suggests the same, as well.
Hopefully, the reader can know understand that the Pattern White Aussie is not the same as the Double Merle or the Double Merles thought to carry “lethal white” genes. Actually, genetically speaking, there is no such thing as a “lethal white.” Nor are they “defective whites,” an equal misnomer. It has been a very sad history in our breed that these two types should have ever been confused at all. Out of ignorance, the Pattern White has been much maligned and completely misunderstood. For the most part there is nothing unsound about this dog, even though it is not accepted in our breed standard. Since many breeders have not understood the difference between the two (pattern white and double merle) the majority of these dogs were unnecessarily destroyed at birth. In fact, out of ignorance, many old-time breeders purposely selected for only solid or self-merle individuals, with no white markings at all, from fear and misunderstanding of the so-called “lethal white” merle genes. Sadly, many pups were destroyed simply because of one white hair!
Fortunately, Dr. Weldon heard, founder of the Flintridge line, did much to explode the myths surrounding the Irish Spotting Pattern versus “lethal white” double merle during the early 60′s. As a veterinarian and livestock breeder, his knowledge of genetic theory led him to suspect, correctly, that the Irish Spotting pattern was responsible for the white trim that we typically see preferred in Aussies today (white collars, socks and blazes) and was completely unrelated to the double merle genes. Dr, Heard identified that the white trim so typical in Collies was inherited consistently and was specific to certain body areas (neck, face and belly). He then used line-breeding to solidify this lovely white trim into our breed.
Nonetheless, when our breed standard was written and adopted, many Aussie breeders did not completely understand the genetics of this breed. Since there was much confusion between the Double Merle and the Pattern White, our standard was written so as to disqualify both – all individuals with excessive white. Since most Pattern Whites are absolutely sound, this was a great shame and disservice to perfectly healthy animals. The Collie Club has come a long way in their understanding of coat color genetics and recognizes the Pattern White as a full-fledged representative of their breed. Similarly, I hope that one day too our breed will re-think its position on Pattern Whites so that healthy pups will not continue to be unnecessarily destroyed at birth. If this article can shed some light on the myth surrounding Pattern Whites, then maybe I have helped bring us all a step closer to a fuller understanding of what they are and why they occur. Pattern Whites are simply a fact of our breed and all Collie-type breeds. So, too, are other colors like sables. What we see in each other’s breed standards are really statements of preference; what colors we like and others we don’t. Most of our standards were based on misinformation and misunderstanding of coat color genetics at the times when they were written. Now that genetic science has become more definitive there is absolutely no reason to fear the Pattern White or put it down as “defective.” It is simply a solid (genotypically) in an overly white suit (phenotypically). Percentages show that it is statistically unlikely to drop dead or be deaf or blind, especially when there is significant pigmentation around the eyes and ears (although I have seen numerous Border Collies with white heads and/or split faces that are as sound as can be.) Most Pattern Whites are perfectly healthy puppies that deserve the love and quality of life we hope for in our other fully recognized Aussies. They are merely blessings of a different color – a color that is in every way a part of our breed.