[2009.02.19] The long and the short and the tall 长的，短的和高的

 

Dog breeds
狗类品种

The long and the short and the tall
长的，短的和高的

Feb 19th 2009 | CHICAGO
From The Economist print edition

What, genetically, distinguishes one breed of dog from another is now becoming apparent
狗类的种间基因差异已经变得明显

A DOG may be man’s best friend. But man is not always a dog’s. Over the centuries selective breeding has pulled at the canine body shape to produce what is often a grotesque distortion of the underlying wolf. Indeed, some of these distortions are, when found in people, regarded as pathologies.

狗是人类最好的朋友，但人却不常是狗最好的朋友。经过几个世纪的选择性育种，狗已经产生与狼一样奇异的变形了。的确，当这种变形在人群中同样出现时，人们将它当成一种疾病。

Dog breeding does, though, offer a chance to those who would like to understand how body shape is controlled. The ancestry of pedigree pooches is well recorded, their generation time is short and their litter size reasonably large, so there is plenty of material to work with. Moreover, breeds are, by definition, inbred, and this simplifies genetic analysis. Those such as Elaine Ostrander, of America’s National Human Genome Research Institute, who wish to identify the genetic basis of the features of particular pedigrees thus have an ideal experimental animal.

狗类繁殖为人们提供了许多机会，来了解控制体型的因素。有关纯种狗祖先的记载相当完备，他们寿命短体型大的特点为研究提供了大量的素材。此外根据定义，品种的基因是先天决定的，这样就更加简化了基因分析的过程。美国国家人类基因研究所的艾莲•奥斯瑞德希望能了解特定血统中表现性征的相关基因根据，那些跟她抱有同样想法的人也同时找到了理想的实验动物。

Dr Ostrander has already used dogs to track down the genes behind certain cancers that the species shares with people, and to work out the dog family tree. At the AAAS she described her search for the genes controlling three of the most important features of a breed: its size, its hair and the length of its legs.

奥斯瑞德博士已经通过对狗的研究发现了基因背后与人共通的特定癌症因素，并构建出狗的族谱。在AAAS（美国艺术与科学研究院）中，她宣布自己找到了控制种类的三个最重要特征的基因：分别控制体型，毛发和腿长。

To investigate size, she looked at a breed called the Portuguese water dog. There are about 10,000 of these animals in North America. All of them are descended from an original population of just 30 that was introduced half a century ago. The size of water dogs, she found, is governed mainly by variations in a gene called insulin-like growth-factor 1—and that is probably true of other breeds as well.

为了研究体型，她着眼于一种葡萄牙水狗。在北美这种动物现存一万只左右，他们全部都是由半个世纪以前的一个的物种进化而成，当时这个物种的数量只有三十只。他发现水狗的体型主要由一种叫做胰岛状生长因子1号决定的，这个发现也会同样适用于其他品种。

Short legs, a phenomenon known as chondrodysplasia, are characteristic of many dog breeds, perhaps most famously dachshunds and corgis. In people the condition is known vulgarly as dwarfism. Dr Ostrander’s work showed that in dogs it is caused by the reactivation of a “dead” version of a gene involved in the regulation of growth. Chromosomes are littered with such non-functional genes; they are the result of mutations favoured by natural selection at some point in the past. Here the gene in question has been reactivated by the arrival within it of what is known as a LINE-1 element. This is a piece of DNA that can jump about from place to place within a genome, sometimes causing havoc as it does so.

软骨发育不良症会导致短腿的现象，这也成为了许多狗类的特征，比如说最出名的德国腊肠犬和威尔士柯基犬。而在人类社会中，人们普遍称拥有此特征的人为矮人。奥斯瑞德博士的研究表明，这种现象是由一种在基因上调节生长的“死亡”信息的再生而导致的。这种没有功能的基因中充满了染色体，这些基因在过去的一段时间中记载着自然选择对物种的改变。这种问题基因在遇到LINE-1素的时候又会恢复活动。LINE-1素可以在染色体组中来回流动，因此有时会造成大的损害。

Woof, woof
汪汪

Dachshunds also featured in her third example—the genetics of dog-hair. Dog coats come in three forms: smooth (ie, short), long and wiry. Some dogs also have what fanciers refer to as “furniture”, notably moustaches. Dr Ostrander found that 80% of the variation between breeds in coat form and furniture was explained by differences in just three genes. Different combinations of these result in different mixtures of coat and furniture.

德国腊肠犬同样适用于她的第三个研究案例――狗的毛发遗传学。狗拥有三种形式的毛皮：光滑的毛（短毛），长毛和卷毛。有些动物还拥有被培育者特别称为“家具”的胡子。奥斯瑞德发现，关于物种毛发和“家具”80％的差异表现在仅仅三个基因上，这些基因的排列组合形成了不同毛发和“家具”的组合。

The upshots of this work are twofold. One is to show that a lot of variety can be caused by only a little genetic variation. Many dog breeds look more different from one another than do the members of groups of real, natural species, so speciation may not be particularly difficult. The second upshot is that dogs may cast light on the condition of human chondrodysplasics and thus prove, once again, what good friends they are to man.

这项研究的结果有两个意义。一者表明许多特征是由少数基因变化决定的，许多饲养狗类的种内差异会大于自然界中真实存在物种的种内差异，因此有关物种形成的研究也没有那么困难。其次，狗类为人类软骨发育异常症研究点亮了明灯，再一次证明了他们是人类的好朋友。

 

译者：Ro.Shepherd  http://www.ecocn.org/bbs/viewthread.php?tid=17499&extra=page%3D1