2020考研英語閱讀理解精讀100篇：Unit 54

Unit 54

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）：本文選自Economist；

注（2）：本文習(xí)題命題模仿對象為2004年真題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.

篇章剖析

本文是一篇說明文，主要說明了研究狗的基因變化對于研究人類疾病的幫助和啟發(fā)。第一段指出狗在長期的育種過程中已經(jīng)出現(xiàn)了很多變形；第二段進一步指出狗類育種幫助人們了解控制體型的因素，以及奧斯瑞德博士的研究發(fā)現(xiàn)了控制某犬種三個最重要特征——體型、毛發(fā)和腿長——的基因；第三至五段分別就這三個方面做出了說明；最后一段則點出了此項研究的雙重意義。

詞匯注釋

canine /?ke?na?n/ adj. 犬的，狗的；似犬的

grotesque /gr???tesk/ adj. 奇形怪狀的；古怪的，怪誕的

pathology /p??θ?l?d?i/ n. 病狀，病變

pedigree /?ped?gri?/ n. 家世，血統(tǒng) adj. 純種的

pooch /pu?t?/ n. 狗

inbred /?in?bred/ adj. 同系交配產(chǎn)生的，種內(nèi)繁殖的

insulin /?insj?l?n/ n. 胰島素

chondrodysplasia n . 軟骨營養(yǎng)障礙，軟骨發(fā)育不良

dachshund /?d?kshund/ n. 臘腸犬

corgis /?k??g?s/ n. 威爾士矮腳狗

dwarfism /?dw??f?z?m/ n. 矮小，侏儒癥

reactivation /?r??kt??ve???n/ n. 再激活

chromosome /?kr??m?s??m/ n. 染色體

havoc /?h?v?k/ n. 大破壞，浩劫

fancier /?f?ns??/ n. （觀賞型動、植物等的）育種者；發(fā)燒友

twofold /?tu?f??ld/ adj. 有兩部分的，雙重的

speciation /?spi?si??e???n/ n. 物種形成

難句突破

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.

主體句式：Those have an ideal experimental animal.

結(jié)構(gòu)分析：本句的主語后面跟了比較復(fù)雜的成分，因此主語與謂語相隔較遠，比較容易造成混淆。其實看到have是復(fù)數(shù)形式就能準(zhǔn)確地判斷出主語應(yīng)該是those。主語后面列舉出Elaine Ostrander作為這類人的代表，緊接著又有兩個結(jié)構(gòu)來對這個人進行補充說明。of引導(dǎo)的短語說明了此人所屬的機構(gòu)，who引導(dǎo)的定語從句則介紹了此人的研究興趣。

句子譯文：研究者們因此有了理想的實驗動物，其中的一位是美國國家人類基因組研究所的伊萊恩·奧斯特蘭德，她希望能確定特定系譜中表現(xiàn)性征的基因基礎(chǔ)。

題目分析

1. B 語義題。文章第二段指出“breeds are, by definition, inbred”。大家一般都熟知breed作動詞時意思是“交配，繁殖”，由此還可以推斷inbred的意思是種內(nèi)的相互交配繁殖。從文中判斷，這種行為是由人類控制的，所以B是正確答案。C項是很有迷惑性的，因為文章雖然討論的動物主要是狗，但是breed還包括其他動物，所以C項不正確。

2. A 細節(jié)題。文章第二段第四句話指出“研究者們因此有了理想的實驗動物，其中的一位是美國國家人類基因組研究所的伊萊恩·奧斯特蘭德，她希望能確定特定系譜中表現(xiàn)性征的基因基礎(chǔ)”，而這種理想的實驗動物就是狗，可見這些人對狗很感興趣，因此A是正確答案。

3. B 推理題。要做對這一題，即使不了解upshot和twofold的意思也無妨，可以通過上下文來判斷。文章最后一段這句話之后是“首先，研究表明了很多特征差異只是由微小的基因變化引起的。許多培育犬種的個體差異要大于自然界中真實物種的種內(nèi)差異，因此物種形成可能沒有那么困難。其次，犬類實驗或許可以幫人們更好地了解人類軟骨發(fā)育異常的問題，而因此再一次證明了它們對人類來說是多么好的朋友”，可見最后一段是討論該研究的兩點意義，因此可以推斷出B是正確答案。

4. A 語義題。引文的意思是“臘腸犬在她的第三例研究——狗的毛發(fā)遺傳中同樣起了重要作用”，也就是說奧斯特蘭德博士又用臘腸犬來開展實驗。所以臘腸犬可以解釋實驗涉及的三個重要特征中的兩點，上一段關(guān)于腿長，這一段則是關(guān)于毛發(fā)，顯然A是正確答案。C和D選項都可以直接排除，而B選項則有一定的干擾作用。該選項的錯誤在于be responsible for，臘腸犬只是有助于理論發(fā)現(xiàn)，而并不是對其負(fù)責(zé)。因此B是錯誤的。

5. C 細節(jié)題。本題針對的是第三、四、五段，這三段分別描述了控制體型、腿長和皮毛的基因。第三段提到“她發(fā)現(xiàn)水犬的體型主要由一種叫做胰島素樣生長因子-1的變異來決定，其他犬種很可能也是如此”，可見A項是正確的。第四段談到了短腿是因為基因的“reactivation”，所以B項也是正確的。第五段提到“奧斯特蘭德發(fā)現(xiàn)，80％的皮毛和‘家具’方面的種間變異僅僅取決于三個基因”，D的表述符合這個意思，故正確。而文章第四段雖然提到“有此特征（短腿）的人俗稱為侏儒”，但后面并沒有提到關(guān)于狗的研究發(fā)現(xiàn)是否也適用于人類，因此C的表述不正確，故選C。

參考譯文

狗也許是人類最好的朋友，但人不總是狗最好的朋友。經(jīng)過幾個世紀(jì)的選擇性育種，狗的外形已經(jīng)發(fā)生了一些古怪的變化。實際上，如果出現(xiàn)在人類身上，某些變形就會被認(rèn)為是病變。

但是，狗類育種確實為那些想要了解如何控制體型的人們提供了一次機會。對純種狗世系系譜的記載相當(dāng)完備，他們生命周期短，窩仔數(shù)大，因此為研究提供了大量素材。此外，育種本質(zhì)上是同系交配，這樣就簡化了基因分析過程。研究者們因此有了理想的實驗動物，其中的一位是美國國家人類基因組研究所的伊萊恩·奧斯特蘭德，她希望能確定特定系譜中表現(xiàn)性征的基因基礎(chǔ)。奧斯特蘭德博士已經(jīng)通過對狗的研究發(fā)現(xiàn)了某些狗和人類都會得的癌癥背后的基因，并繪出了狗的家系圖。她向AAAS（美國科學(xué)促進會）描述了自己的實驗，尋找控制某犬種三個最重要特征——體型、毛發(fā)和腿長——的基因。

為了研究體型，她以一種稱為葡萄牙水犬的犬種作為研究對象。北美約有一萬只這種動物。它們都是半個世紀(jì)以前被帶到北美的三十條水犬的后代。她發(fā)現(xiàn)水犬的體型主要由一種叫做胰島素樣生長因子-1的變異來決定，其他犬種很可能也是如此。

短腿——軟骨發(fā)育不良的病征，是許多犬種的特征，最出名的大概是臘腸犬和威爾士矮腳狗。而有此特征的人俗稱為侏儒。奧斯特蘭德博士的研究表明，犬類短腳是由于調(diào)節(jié)生長有關(guān)的一種基因的“死亡”變異型再度被激活。染色體中布滿了這種沒有功能的基因，它們是過去的某個時候自然選擇導(dǎo)致的變異結(jié)果。此處討論的這個基因在遇到被稱為LINE-1的物質(zhì)時會被激活。LINE-1是一個DNA片段，可以在染色體組中四處移動，有時會在移動中造成破壞。

臘腸犬在她的第三例研究——狗的毛發(fā)遺傳中同樣起了重要作用。狗的皮毛有三種形式：光滑的毛（短毛）、長毛和卷毛。有些狗還有被育種者稱為“家具”的特征，尤其是胡子。奧斯特蘭德博士發(fā)現(xiàn)，80％的皮毛和“家具”方面的種間變異僅僅取決于三個基因，這些基因的組合變化產(chǎn)生了皮毛和“家具”的不同組合。

這項研究的結(jié)果有雙重意義。首先，研究表明了很多特征差異只是由微小的基因變化引起的。許多培育犬種的個體差異要大于自然界中真實物種的種內(nèi)差異，因此物種形成可能沒有那么困難。其次，犬類實驗或許可以幫人們更好地了解人類軟骨發(fā)育異常的問題，而因此再一次證明了它們對人類來說是多么好的朋友。