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《考研英语阅读理解100篇 基础版》第4章 科学研究类 Unit 54

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2019年01月15日

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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 grotesque distortion.Indeed,some of these distortions are,when found in people,regarded as pathologies. 
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. 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. 
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. 
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. 
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. 
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 chondrodysplasia and thus prove,once again,what good friends they are to man. 
注(1):本文选自Economist; 
注(2):本文习题命题模仿对象为2004年真题Text 3。 
1.The expression“breeds” (Line 3,Paragraph 2)most probably means ______. 
A) natural species 
B) animals developed by people 
C) inbred dogs 
D) domesticated animals 
2.The attitude of those who wish to identify the genetic basis of the features of particular pedigrees towards dogs is one of ______. 
A) enthusiastic interest 
B) reserved indifference 
C) slight doubt 
D) strong contempt 
3.By saying“the upshots of this work are twofold”(Line 1,Last Paragraph),the author implies that ______. 
A) the research is divided into two parts 
B) the research is important in two senses 
C) the results of the research involve two types of dogs 
D) the research has achieved two important results 
4.What does the author mean by saying“Dachshunds also featured in her third example—the genetics of dog-hair”(Line 1,Paragraph 5)? 
A) Dachshunds can also explain another aspect of Dr Ostrander's theory. 
B) Dachshunds are responsible for two aspects of Dr Ostrander's theory. 
C) Dachshunds feature special genes of hair. 
D) Dachshunds are special because of their distinctive hair. 
5.Which of the following is NOT true according to the passage? 
A) What was found about the Portuguese water dog is likely applicable to other dogs as well. 
B) Short legs in dogs have something to do with gene reactivation. 
C) What was found about chondrodysplasia in dogs can also apply to dwarfism in human. 
D) The variation of dog coat does not involve a large quantity of genes but only a few. 

狗也许是人类最好的朋友,但人不总是狗最好的朋友。经过几个世纪的选择性育种,狗的外形已经发生了一些古怪的变化。实际上,如果出现在人类身上,某些变形就会被认为是病变。 
但是,狗类育种确实为那些想要了解如何控制体型的人们提供了一次机会。对纯种狗世系系谱的记载相当完备,他们生命周期短,窝仔数大,因此为研究提供了大量素材。此外,育种本质上是同系交配,这样就简化了基因分析过程。研究者们因此有了理想的实验动物,其中的一位是美国国家人类基因组研究所的伊莱恩·奥斯特兰德,她希望能确定特定系谱中表现性征的基因基础。奥斯特兰德博士已经通过对狗的研究发现了某些狗和人类都会得的癌症背后的基因,并绘出了狗的家系图。她向AAAS(美国科学促进会)描述了自己的实验,寻找控制某犬种三个最重要特征——体型、毛发和腿长——的基因。 
为了研究体型,她以一种称为葡萄牙水犬的犬种作为研究对象。北美约有一万只这种动物。它们都是半个世纪以前被带到北美的三十条水犬的后代。她发现水犬的体型主要由一种叫做胰岛素样生长因子-1的变异来决定,其他犬种很可能也是如此。 
短腿——软骨发育不良的病征,是许多犬种的特征,最出名的大概是腊肠犬和威尔士矮脚狗。而有此特征的人俗称为侏儒。奥斯特兰德博士的研究表明,犬类短脚是由于调节生长有关的一种基因的“死亡”变异型再度被激活。染色体中布满了这种没有功能的基因,它们是过去的某个时候自然选择导致的变异结果。此处讨论的这个基因在遇到被称为LINE-1的物质时会被激活。LINE-1是一个DNA片段,可以在染色体组中四处移动,有时会在移动中造成破坏。 
腊肠犬在她的第三例研究——狗的毛发遗传中同样起了重要作用。狗的皮毛有三种形式:光滑的毛(短毛)、长毛和卷毛。有些狗还有被育种者称为“家具”的特征,尤其是胡子。奥斯特兰德博士发现,80%的皮毛和“家具”方面的种间变异仅仅取决于三个基因,这些基因的组合变化产生了皮毛和“家具”的不同组合。 
这项研究的结果有双重意义。首先,研究表明了很多特征差异只是由微小的基因变化引起的。许多培育犬种的个体差异要大于自然界中真实物种的种内差异,因此物种形成可能没有那么困难。其次,犬类实验或许可以帮人们更好地了解人类软骨发育异常的问题,而因此再一次证明了它们对人类来说是多么好的朋友。 
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