One of the most unique coat color patterns in the domestic dog is merle (also known as dapple in the dachshund breed), characterized by patches of normal pigmentation surrounded by diluted eumelanin pigment. In dogs, this striking variegated pattern is caused by an insertion of a SINE element into the PMEL gene. Differences in the length of the SINE insertion [due to a variable-length poly(A)-tail] has been associated with variation in the merle coat color and patterning. We previously performed a systematic evaluation of merle in 175 Australian shepherds and related breeds and correlated the length of the merle insertion variants with four broad phenotypic clusters designated as “cryptic”, “atypical”, “classic”, and “harlequin” merle. In this study, we evaluated the SINE insertions in 140 dachshunds and identified the same major merle phenotypic clusters with only slight variation between breeds. Specifically, we identified numerous cases of true “hidden” merle in dachshunds with light/red (pheomelanin) coats with little to no black/brown pigment (eumelanin) and thus minimal or no observable merle phenotype. In addition, we identified somatic and gonadal mosaicism, with one dog having a large insertion in the harlequin size range of M281 that had no merle phenotype and unintentionally produced a double merle puppy with anophthalmia. The frequent identification of cryptic, hidden, and mosaic merle variants, which can be undetectable by phenotypic inspection, should be of particular concern to breeders and illustrates the critical need for genetic testing for merle prior to breeding to avoid producing dogs with serious health problems.

家犬最独特的毛色图案之一是陨石色（在腊肠犬品种中也称为斑纹），其特征是正常色素沉着斑块被稀释的真黑色素色素包围。在狗中，这种引人注目的杂色图案是由将 SINE 元素插入PMEL 引起的基因。SINE 插入长度的差异 [由于可变长度的 poly(A) 尾] 与陨石色毛色和图案的变化有关。我们之前对 175 只澳大利亚牧羊犬和相关品种的陨石色进行了系统评估，并将陨石色插入变体的长度与四个广泛的表型集群相关联，这些表型集群被指定为“隐匿”、“非典型”、“经典”和“丑角”陨石色。在这项研究中，我们评估了 140 只腊肠犬的 SINE 插入，并确定了相同的主要陨石色表型簇，但品种之间只有轻微的差异。具体来说，我们在腊肠犬中发现了许多真正的“隐藏”陨石色案例，它们具有浅色/红色（褐黑素）皮毛，几乎没有或没有黑色/棕色色素（真黑素），因此很少或没有可观察到的陨石色表型。此外，我们确定了体细胞和性腺嵌合现象，其中一只狗在 M281 的丑角大小范围内有一个大插入，没有陨石色表型，并且无意中产生了一只患有无眼症的双陨石色小狗。经常发现隐匿的、隐藏的和镶嵌的陨石色变种，这些变种可能无法通过表型检查检测到，育种者应该特别关注，并说明在繁殖前对陨石色进行基因检测的迫切需要，以避免产生具有严重健康问题的狗。