white by piebald spotting (-/s) or the limited white markings of S/S animals. It does not affect white areas that were caused by a/a e/e or M/M or M/m H/h. The colour of the tick marks will be as expected or one shade darker. Tick marks are semi-random, so that they vary from one dog to the next and can overlap, but are generally present on the lower legs and heavily present on the nose. U (urajiro) locus The alleles at the theoretical U locus are thought to limit phaeomelanin production on the cheeks and underside. Two alleles are theorized to occur at the U locus: U = Urajiro u = Not urajiro It is thought that U is recessive to u but due to lack of genetic studies these assumptions have only been made through visual assessment. The urajiro pattern is expressed in the tan (phaeomelanin) areas of any dog and does not effect black (eumelanin) pigment. Miscolours in dog breeds Miscolours occur quite rarely in dog breeds, because genetic carriers of the recessive alleles causing fur colours that don't correspond to the breed standard are very rare in the gene pool of a breed and there is an extremely low probability that one carrier will be mated with another. In case two carriers have offspring, according to the law of segregation an average of 25% of the puppies are homozygous and express the off-colour in the phenotype, 50% become carriers and 25% are homozygous for the standard colour. Usually off-coloured individuals are excluded from breeding, but that doesn't stop the inheritance of the recessive allele from carriers mated with standard-coloured dogs to new carriers. In the breed Boxer large white markings in heterozygous carriers with genotype S si or S sw belong to the standard colours, therefore extreme white Boxers are born regularly, some of them with health problems. The cream-white colour of the Shiba Inu is not caused by any spotting gene but by strong dilution of pheomelanin. Melanocytes are present in the whole skin and in the embryonic tissue for the auditory organs and eyes, therefore this colour is not associated with any health issues. The occurrence of a dominant coat colour gene not belonging to the standard colours is a suspicion for crossbreeding with another breed. For example the dilute gen D in the suddenly appeared variety "silver coloured" Labrador Retriever might probably come from