The 20S proteasome β2 subunit (PSMB7) gene is responsible for the Harlequin coat pattern in Great Danes. This gene is also known as H-Locus. Harlequin is a pattern resulting from interaction of the Merle (M-locus) gene and the Harlequin (H-locus) gene on black pigment. The Harlequin gene can modify the Merle gene. The Harlequin pattern is only expressed if on the M-locus at least one copy of the M allele is present in combination with at least one copy of the E or Em allele on the E-locus. Dogs that are not merle, or only have red pigment, cannot express the Harlequin gene. The dominant Merle gene, by itself produces dark spots on a diluted background. If a Merle dog also inherits one copy of the Harlequin gene, the dark spots increase in size and the background pigment is removed (turns white). The Harlequin mutation in Great Danes is in homozygous state (two copies of the mutation) considered embryonic lethal as no live dogs with two copies of the mutation have been observed. This means that pups that are homozygous for the Harlequin mutation do not develop in the uterus and are reabsorbed very early in the development process. Therefore all Harlequin patterned dogs have only 1 copy of the Harlequin mutation. The Coat colour H-locus (Harlequin) test (H316) tests for the genetic status of the H-locus. This gene has two variants (alleles), H and N. The allele H is dominant. One copy of the H allele, together with at least one copy of both the M allele for the M-locus and the E allele for the E-locus results in dogs with the Harlequin pattern. Two copies of the H allele result in early embryonic death. The allele N does have no effect on the coat colour.
The Coat colour H-locus (Harlequin) test encloses the following results.
|N/N||No Harlequin pattern unless modified by other colour modifying factors, only allele N will be passed on to an offspring|
|N/H||Harlequin mutation is present. In order to express the Harlequin pattern the dog must carry at least one copy of both the M-allele for the M-locus and the E-allele for the E-locus. Either allele N or P will be passed on to an offspring|