Like other domesticated species, dogs show great diversity in the coloring and patterning of their coats. During domestication and breed formation, genes responsible for these phenotypes underwent strong selective pressure, including the pigmentationgenePMEL(akaSILV). PMEL is a protein found in specialized organelles responsible for producing the black and brown pigments that give hair its color.

梅尔外套的遗传学

Heterozygosityfor aShort INterspersed Element (SINE) insertion in caninePMELcauses a striking pigmentation pattern, known as梅尔，这是驯养的狗独有的。正弦是一种逆转录座子, a “mobile” DNA element that can be copied and pasted into a new location in the genome. The most common canine SINE is about200 base pairs（bp）长，尾端有一大堆腺嘌呤碱基。插入PMELSine是一次在具有表型的各种品种的共同祖先中发生的事件，其中包括几种放牧品种，大丹麦人和腊肠犬。

A standard merle coat has two characteristics: a diluted base color and random patches of full pigmentation. In recent years, two spontaneous variations of merle have been recognized: dilute and harlequin. Dilute merles have a milder coat dilution with no patches. Harlequin merles have a white background with large patches of full pigmentation.

在这个study published today in移动DNA, we sequencedPMELin dilute and harlequin merle dogs and found that variation exists only in the number of adenine bases in the tail of the SINE. We refer to this variable region as “oligo(dT)” because the SINE was inserted in reverse orientation relative toPMEL，resulting in a run of thymine bases at the beginning of the insertion. The梅尔(M) SINE has an unusually long and pure oligo(dT).

Understanding variations in coat dilution and patches

为了了解正弦（称为寡核（DT））变量区域的长度与梅尔外套的物理特征之间的关系，我们研究了259只Merle狗（使用杂合基因型毫米) in which we observed 36 different oligo(dT) lengths. Dogs having the shortest lengths did not display the merle phenotype; these dogs are termed cryptic merles (since they are technically genetically merle, but don’t appear to be). Standard merle dogs possessed lengths from 78 to 86 bp. Dilute merles had lengths intermediate to cryptic and standard merles, while harlequin merles had the longest lengths (See Figure above. Note: We report an individual dog’s oligo(dT) length as a superscript number in the genotype (e.g。M⁷⁹m.))

当我们分别考虑Merle模式的两个特征时，我们发现基本外套的稀释或闪电出现在独特的寡核（DT）长度阈值下。涂层稀释开始发生在56至66 bp之间，并且随着寡核（DT）的增加而增加，使得长度为87 bp或更长时间的狗具有某些或完全的异形（也就是说,loss of color) of their base coat.

完全色素沉着的斑块开始出现，寡核（DT）长度在75至78 bp之间。我们假设在开发过程中，这些长段的复制滑倒会导致频繁的随机截断会导致稳定的隐秘Merle Oligo（DT）长度。Somatic cellpopulations in which the oligo(dT) length has reverted to cryptic merle lengths produce normal PMEL protein, resulting in patches of full pigmentation.

较长的寡核能（DT）长度较不稳定，并且在开发过程中经历更频繁的恢复。有些狗的色素沉着很大，乍看之下，它们似乎是非狗的狗。其他人则对各种寡核（DT）的长度进行了多个体细胞反向，产生了带有一系列稀释强度的大斑块，有时被称为花呢。代表体逆转的寡核（DT）长度在括号中表示（例如，遗传了86 bp但具有可检测到45 bp的可检测到的体细胞的狗（dt）的狗。M⁸⁶m(M⁴⁵)).

Implications of merle phenotypes for dog owners and breeders

Spontaneous changes in oligo(dT) length can also occur in thegermline, such that a standard merle dog can produce a “surprise” dilute or harlequin merle puppy. The dilute merle phenotype resembles the characteristic grey coat of a recessive disease of collies,环状中性粒细胞减少症，这需要幼犬人道的安乐死。哈勒奎因梅尔（Merle）可以类似于另一个常见的外套图案，piebald, which can be troublesome for breeders in countries or breed clubs where this phenotype is prohibited.

尽管梅尔是狗最受欢迎的外套图案之一，但这并非没有争议。Merle-to-Merle Matings可能会导致双重MERLE（毫米) offspring that have ocular (including blindness andmicrophthalmia) and auditory defects; this is possible even for merle-to-cryptic merle matings. We hope this work will raise awareness among breeders that there are merle varieties that do not fit the standard phenotypic description and that this knowledge will prevent undesirable matings and mischaracterizations.