长句分析：The chanceof a sexually reproducing organism’s offspring inheriting a particular version of a gene from a particular parent is 50%.
句子的主体很简单，就是The chance is 50%. 那么是什么几率为50%呢？
中间的部分给出了介绍：是有性生殖生物的后代某一种行为的几率为50%。
那么是什么行为呢？再一个动词现在分词做状语：从两亲的特定一方遗传到一个特定基因型的概率，为50%
所以综合起来，这句话的意思就是：
有性生殖生物的后代从两亲特定一方遗传到某一特定基因型的几率是50%
promising：showing signs of being successful or good in the future
大有希望的，很有前途的
a promising career in law
很有前途的法律界事业
favour A over B: have partiality for sth,but not to love it
偏爱…而不喜欢…:
A coach should not favor oneplayer over another on the team.
教练不应偏爱队里的某个球员,而不喜欢另一个。
2
可为人类所用，但难度极大
Researchers realised, soon after the discovery of gene drives half a century ago, that they might be forged intotools for eradicating diseases and pests. For example, a drive promulgating a genetic variant that made mosquitoes unable to host the parasite that causes malaria could be used to help eliminate the disease. If the propagating variant made female mosquitoes sterile, it might provide a means to eliminate the troublesome insects themselves.
Engineering gene drives to do humanity’s biddingin this way proved, however, devilishlydifficult.The idea therefore languisheduntil 2015, when Valentino Gantz and Ethan Bier of the University of California, San Diego, used CRISPR-Cas9, a recently discovered gene-editing tool, to make a gene drive that could be inserted anywhere in a targetgenome that they chose.
forge: to put a lotof effort into making sth successful or strong so that it will last
Everything new comes from theforge of hard and bitter struggle.
一切新的东西都是从艰苦斗争中锻炼出来的。
promulgating:to spread an idea or belief to as many people as possible
传播〔思想或信仰〕
do someone’s bidding:submit to someone’sorders; perform services for someone
（尤指奴颜婢膝地）服从某人，听命于某人，为某人效劳
After he took over the department, he expected everyone around him to do his bidding.
自从他当了部门主管之后，就希望所有的人都拍他的马屁。
devilishly:very – used to show that you think something is annoying or bad
非常，极其〔表示某物讨厌或糟糕〕
•a devilishly difficult task
非常困难的任务
languished 憔悴，潦倒;（草木等）凋萎; 失去活力; 烦恼，焦思
Without the founder's drive and direction, the company gradually languished.
没有了创始人的斗志与指引，公司逐渐走向没落。
genome:all the genesin one cell of living thing
•the human genome
人类基因组
３
基因驱动的潜在危害
Those findings sparked concerns about the effects gene-drive-carrying organisms could have if they were ever to be released into the world. For example, a gene drive that somehow hoppedfrom a target species into the genomes of other animals might wipe them outbefore anything could be done about it. A study published in PLOS Genetics, by Philipp Messer of Cornell University and his colleagues suggests, however, that those who would deploy gene drives against scourgessuch as malaria face a more immediate hurdle: such drives simply may not work. Just as insects and pathogensevolve resistance to new pesticides and antibiotics, so gene drives, too, may provoke resistance—and may do so far faster than many suspected.
Hop from sth to sth:to change from one activity or subject to another
I like to hop fromchannel to channel when I watch TV.
我看电视的时候喜欢换台
wipe out: to destroy,remove, or get rid of something completely
彻底毁灭; 勾销; 去除，抹去
Whole villages werewiped out by the floods.
整个整个的村庄被洪水吞没。
scourge: something that causesa lot of harm or suffering
祸根，祸害
•the scourge of unemployment
失业的祸根
pathogen: something that causes disease in your body
病原体，致病菌
4
自然条件下CRISPR-Cas9的工作原理
Life finds a way
In nature, elements of the CRISPR-Cas9 system help bacteria to ward off viral infections. Some viruses replicate themselves by inserting their DNA into the genomes of their hosts. This hijacks a cell’s protein-making machinery, causing it to turn out components for new viruses. CRISPR-Cas9 selectively excises such foreign DNA, eliminating the invaders.
The excision mechanism consists of two molecules: an enzyme (Cas9) derived froma bacterium called Streptococcus pyogenes, and a piece of RNA, a chemical akin toDNA that is made up of similar genetic letters. This “guide” RNA will stick only to a section of DNA with a letter-sequence complementary to its own. The enzyme is bound to the guide RNA. The guide RNA is bound to the DNA. Hence the enzyme recognises the DNA it has to cut, and snips it at the correct location. By inserting the gene for Cas9 into an organism, together with genetic material that instructs a cell to produce the correct guide RNA, biologists can therefore use CRISPR-Cas9 to sever a genome at a specific point.
They can then insert at that point whatever payload of other genes they might like—to modify mosquitoes so they cannot transmit diseases, say—knowing that the cell’s DNA-repair mechanisms will subsequently kick in to repair the incision around the newly inserted genes.
Handily, the system works in any organism, not just the bacteria in which Cas9 is found naturally. To use it as a gene drive, all that is required is to include in the payload the genes for the CRISPR-Cas9 system itself, and to ensure that some copies get inserted into an organism’s germcells—those that develop into sperm or eggs. This will mean that the gene driveis passed on to all of that organism’s offspring.
ward off: to do something totry to protect yourself from something bad, such as illness, danger, or attack
防止，抵挡〔疾病、危险、攻击等〕
Don't forget insectrepellent to ward off the mosquitoes.
别忘了带上防蚊子的驱虫剂。
derive from: to get a chemicalsubstance from another substance
提取〔化学物质〕
The enzyme is derivedfrom human blood.
这种是从人体血液中提取的。
akin to: very similar to something
与某物相似的，与某物类似的
Something akin topanic overwhelmed him.
一种类似惊恐的感觉使他不知所措。
genetic letters/letter sequence: 这里的letter也翻译成字母，但它指的是基因序列中一个个单独的基因，具体可以叫做genetic lettter基因字母，而letter sequence指的其实就是genetic letter sequence，即基因序列
snips: to cut something by making quick cuts with scissors
〔用剪刀〕迅速地剪
I snipped the stringand untied the parcel.
我剪断绳子，解开包裹。
payload: the amount of goods or passengers that can be carried by a vehicle, or the goods that a vehicle is carrying
〔运输工具的〕最大载荷，有效载荷; 〔运输工具的〕装载货物;
The helicopter isdesigned to carry a payload of 2640 pounds.
这种直升机设计的最大载荷为2640 磅。
handily: something that is handily placed is in a position where it can easily be reached or used
手边; 附近
She kept the keyhandily by the back door.
她把钥匙挂在后门方便拿取。
5
CRISPR-Cas9的弊端
CRISPR-Cas9 gene drives have, though, a significant drawback.When the drive cuts the genome but fails, for some reason, to insert itself into the incision, the cell instead inserts new genetic letters to replace those cut away by the enzyme before it rejoins the severed DNA strands. This process often changes the letter sequenceat the site. That means the guide RNA can no longer recognise it. And that, in turn, means the organism (and its progeny) are now resistant to the drive.
drawback:a disadvantage of asituation, plan, product etc
缺点，毛病; 不利因素
It's a great city –the only drawback is the weather.
这是座很不错的城市，唯一的不足就是天气。
progeny：the babies of animals or plants
〔动植物的〕后代，后裔;
６
果蝇实验证明弊端存在
Dr Messer wanted to understand this process. To do so, he and his colleagues observed the effects of introducing a CRISPR-Cas9 gene drive they had developed into fruitflies—insects commonly used in genetic studies.
Their drive’s payload was a gene that encodes red fluorescent protein, a substance normally found in a species of sea anemone. By further genetic tweaking, the researchers arranged for this protein to be expressed, in particular, in the insects’ eyes. They thus knew that flies with fluorescent eyes carried their gene drive. Also, the guide RNA they selected meant the drive inserted this payload into the middle of a gene named “yellow”, thus disrupting that gene’s action. Flies which inherit a defective version of “yellow” have yellow bodies, rather than black ones.
After experiments with thousands of flies, Dr Messer and his team found that the gene drive successfully inserted itself into the insects’ DNA about half the time, producing flies with fluorescent eyes and yellow bodies. The other half of the insects nearly all had yellow bodies, but did not have fluorescent eyes. That indicated CRISPR-Cas9 had cut the DNA in the right place, thus disrupting the function of “yellow”, but had failed to insert itself into the incision. Sequencing the genomes of these flies confirmed that in virtually all cases the consequence was a mutation that rendered the flies (and would have rendered any offspring) resistant to the gene drive.
这个实验干了个什么事呢？
用来做切割刀的基因CRISPR-Cas9的负载基因上有红眼基因，而rRNA则会识别果蝇体内的“yellow”基因，这个yellow基因的有趣之处在于，只有它被破坏了，果蝇才会有黄色的身体。
所以如果实验结果，果蝇有黄色身体，就表明CRISPR-Cas9成功完成了切割，即破坏了yellow基因。如果果蝇有红眼，就表明CRISPR-Cas9成功把自己（加上负载基因）植入到被切割的部位，使果蝇有了红眼。
当然，实验结果是一半左右既有红眼又有黄色身体，另一半则只有黄色身体而没有红眼。这就表明，的确CRISPR-Cas9有上文提到的缺点：即存在只切割而没有植入的情况。
７
实验室ｖｓ野外环境带来的新挑战
Red signal
The team then repeated their experiments with fruitfly lines from five continents. They found that the proportion of flies becoming resistant to the drive varied from about 60% down to 4%. Differences in resistance to the drive were not caused by any initial differences in the target sequence. That did not vary between the five lines. They must therefore have stemmed from other (as yet unknown) genetic differences between the flies. This is a worry because it suggests that even if a drive works well in laboratory animals, it may fail in the wild when it encounters populations with higher resistance. Getting to the bottom of what is causing some lines to be more resistant than others will be an important step towards the development of gene drives that can spread traits through a species, Dr Messer reckons.
stem from：to develop as aresult of something else
源于，来自; 由…发生:
His headaches stemmedfrom vision problems.
他的头痛是由视力问题引起的。
get to the bottom of：find the origin or cause of something
找出事情/(問題)的根源。
The previous proposal couldn't resolve the efficiency of IT department. We have toget to the bottom of this.
trait：a particular qualityin someone's character
〔某人性格中的〕特性，品质:
a mental illnessassociated with particular personality traits
和某些性格特征有关的精神疾病
genetic / inherited traits
遗传的性格特征
８
应对之策亦有二
Two further modifications of CRISPR-Cas9 gene drives may help. The first is to equip them with several guide RNAs, allowing Cas9 to cut chromosomes（染色体） at more than one place. An organism would have to develop resistant DNA sequences at all of these to become fully immune to the drive. Dr Messer and his colleagues have made such a drive, containing two guide RNAs, and have found that it did indeed lower the proportion of flies that developed resistance—though estimates made with computer models suggest this is still not enough for the drive to reach more than about half the population.
The second approach is to put the drive into the middle of a gene that, unlike “yellow”, an organism needs to survive. This might be expected to disrupt the gene and kill the organism. But if the inserted DNA has, at one end, a replica of the part of the disrupted gene that has been displaced by the insertion, this can meld seamlessly（无缝连接）with its counterpart in the animal, preserving the gene’s function and Cas9’s ability to recognise it. If the join is not seamless, though, the gene will fail and the animal will die. Mutant genes resistant to the drive will thus be unable to spread.
At least two groups, one based at Imperial College, in London, and the other at Harvard University and the Massachusetts Institute of Technology, are working on drives aimed at essential genes in mosquitoes and which use multiple guide RNAs. If they succeed, they will breathe new life into the field. As Dr Messer observes,“it is difficult to cheat evolution.” Whether it is impossible to do so remains to be seen.
应对之策之一：携带多对识别用的ＲＮＡ，这样就算某一处切断了没植入也有其他地方可以植入，加大了成功几率：
应对之策之二：破坏的（即识别的）对象基因是生物存活必需的基因，那么如果植入失败，那对象基因也无法发挥功能，那么这类本该对基因驱动产生抗性的生物就会死亡而被淘汰。
返回搜狐，查看更多