一本教会你“做对”题的6级阅读书 day7 passage4
Passage 4 Gene Silencing 125
基因“沉默” 《卫报》
[00:00]Silencing a gene is a well established technique in mice,
[00:05]where it is used to create so-called "knockout" mice
[00:09]to study the effects of genes.
[00:12]Artificial DNA is introduced into the mouse embryonic stem cells
[00:17]to silence one particular gene.
[00:20]The altered cells are then introduced into early mouse embryos,
[00:25]which are then implanted in a mouse womb.
[00:29]The resulting pups have some tissues with altered genes,
[00:33]but repeated breeding ensures mice that have all their tissues of the new type.
[00:40]But very few genes have single effects
[00:44]and altering one can have deadly consequences.
[00:48]About 15% of mouse gene knockouts are lethal;
[00:53]others produce unexpected handicaps.
[00:57]In humans there is a gene that appears to
[01:00]be correlated with a 10-point boost in IQ.
[01:04]But it is also associated with a 10% chance of developing a muscle condition
[01:11]that can confine the sufferer to a wheelchair with uncontrollable muscle spasms.
[01:17]Altering genes isn't like editing a document in Word.
[01:23]DNA is an invisibly thin molecule coiled upon itself
[01:28]with the millions of letters
[01:30]that we can't see trying to alter just three letters
[01:35]without damaging anything else is a truly daunting task.
[01:40]These dangers mean that designer babies are not possible now and may never be.
[01:47]Building a new organism from scratch is possible.
[01:52]In January this year a US team reported in Science magazine
[01:58]how it built the entire DNA code of a common bacterium in the laboratory
[02:05]using blocks of genetic material.
[02:08]The team synthesized small blocks of DNA
[02:12]before knitting them together into bigger "cassettes" of genes.
[02:18]Large chunks of genes were joined together
[02:22]to make the circular genome of a synthetic version of a mycoplasma bacterium.
[02:29]This technique is called synthetic biology
[02:33]and it combines science and engineering
[02:37]to build new biological functions and systems.
[02:41]The US group J Craig Venter Institute hopes eventually
[02:47]to use engineered genomes to make bacteria that can do useful things,
[02:54]such as produce clean fuels or take carbon dioxide out of the atmosphere.
[03:00]But many people are extremely concerned
[03:04]by the possibilities of bio-error (or bio-terror) that artificial life creates.
[03:11]They say artificial microbes could have dangerous consequences
[03:16]if they escape into the environment or
[03:19]if they are used to manufacture bio-weapons.
[03:23]At present there are no international laws or oversight mechanisms
[03:29]to assess the safety of synthetic organisms.
[03:33]Organizations such as the Royal Society
[03:36]are currently seeking the public's view on this technology.
