首页
外语
计算机
考研
公务员
职业资格
财经
工程
司法
医学
专升本
自考
实用职业技能
登录
外语
If you go down to the woods today, you may meet high-tech trees—genetically modified to speed their growth or improve the qualit
If you go down to the woods today, you may meet high-tech trees—genetically modified to speed their growth or improve the qualit
admin
2018-08-25
14
问题
If you go down to the woods today, you may meet high-tech trees—genetically modified to speed their growth or improve the quality of their wood. Genetically-engineered food crops have become increasingly common, albeit controversial, over the past ten years. But genetic engineering of trees has lagged behind.
Part of the reason is technical. Understanding, and then altering, the genes of a big pine tree are more complex than creating a better tomato. While tomatoes sprout happily, and rapidly, in the laboratory, growing a whole tree from a single, genetically altered cell in a test tube is a tricky process that takes years, not months. Moreover, little is known about tree genes. Some trees, such as pine trees, have a lot of DNA—roughly ten times as much as human. And, whereas the Human Genome Project is more than half-way through its task of isolating and sequencing the estimated 100, 000 genes in human cells, similar efforts to analyze tree genes are still just saplings(幼苗).
Given the large number of tree genes and the little that is known about them, tree engineers are starting with a search for genetic "markers". The first step is to isolate DNA from trees with desirable properties such as insect resistance. The next step is to find stretches of DNA that show the presence of a particular gene. Then, when you mate two trees with different desirable properties, it is simple to check which offspring contain them all by looking for the genetic markers. Henry Amerson, at North Carolina State University, is using genetic markers to breed fungal resistance into southern pines. Billions of these are grown across America for pulp and paper, and outbreaks of disease are expensive. But not all individual trees are susceptible. Dr. Amerson’s group has found markers that distinguish fungus-resistant stock from disease-prone trees. Using traditional breeding techniques, they are introducing the resistance genes into pines on test sites in America.
Using genetic markers speeds up old-fashioned breeding methods because you no longer have to wait for the tree to grow up to see if it has the desired traits. But it is more a sophisticated form of selective breeding. Now, however, interest in genetic tinkering(基因修补)is also gaining ground. To this end, Dr. Amerson and his colleagues are taking part in the Pine Gene Discovery Project, an initiative to identify and sequence the 50,000-odd genes in the pine tree’s genome Knowing which gene does what should make it easier to know what to alter.
It is discovered by Henry Amerson’s team that_____.
选项
A、southern pines cannot resist fungus
B、all southern pines are not susceptible
C、the genetic marker in southern pines was the easiest to identify
D、fungus-resistant genes came originally from outside the U.S.A.
答案
B
解析
选项B是一个半否定的句式,因此本题关键在于理解选项B的All…are not…结构在意义上等同于第3段倒数第3句的not all…are….第3段倒数第2句中的fungus-resistant stock指的是南方松树中能抗真菌的树种,并非别的与南方松树毫不相关的树种,因此A的说法不正确。
转载请注明原文地址:https://kaotiyun.com/show/CHH7777K
0
大学英语六级
相关试题推荐
Electronictrash,knownase-waste,ispilingupfasterthaneverinAmericanhomesandbusinesses.Peopledonotknowwhattod
Theselfishnessofhumansisacentralassumptionoforthodox(传统的)economics,whereitisthoughttoleadtobenefitsfortheeco
Theselfishnessofhumansisacentralassumptionoforthodox(传统的)economics,whereitisthoughttoleadtobenefitsfortheeco
RisingInequalityIsHoldingBacktheU.S.Economy[A]Inannouncinghisrunforthepresidencylastmonth,JebBushhassetan
GetWhatYouPayFor?NotAlways[A]ThemostexpensiveelectioncampaigninAmericanhistoryisover.ExecutivesacrossAmer
Baby-NamingTrends[A]Overthelastfiftyyears,Americanparentshaveradicallyincreasedthevarietyofnamestheygiveth
ConradHiltonreallywantedtobeabanker.Instead,hesuccessfullychangedthe【C1】______purchaseofaTexaslow-endhotelinto
Parentscaneasilycomedownwithanacutecaseofschizophrenia(精神分裂症)fromreadingthecontradictoryreportsaboutthestateof
The35-year-oldBeijingwomaniswatchinganadshowingagianttelevisionmadebytheChinesecompanyHaier.Astreamofintrod
Somefuturologistshaveassumedthatthevastupsurge(剧增)ofwomenintheworkforcemayportendarejectionofmarriage.Manyw
随机试题
利息来源于()
下列符号中,表示数据结构中可重复项的是()
下述哪项不属于原始骨痂形成期范围
患者男,72岁。因进食时误吞鸭骨后吞咽困难和吞咽疼痛6小时,在当地医院就诊,经照X线片发现食管中段有不透光的阴影,由于当地医院条件有限,仅给予抗感染、对症和支持治疗两天,症状无明显缓解,且出现背部及胸骨后疼痛,多次呕吐,呕吐物为唾液样物,其中两次带有少许鲜
《入境货物报检单》上的货物总值应与()上所列的一致。
电脑上的数字图像可根据其不同特性分为两大类。一类是(),一类是点阵图。
外国旅游者要求中途退团或延长旅游时,都必须()。
尊阿弥陀佛为教主,以向往西方极乐世界为宗旨的佛教教派是()。
下列工具中为需求分析常用工具的是______。
What’stheproblemtheworldisnowfacing?Theworldisnotonlyhungrybutitisalso______.
最新回复
(
0
)