《考研英語閱讀理解100篇 基礎(chǔ)版》第4章　科學(xué)研究類 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.