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》
Silencing a gene is a well established technique in mice,
where it is used to create so-called "knockout" mice
to study the effects of genes.
Artificial DNA is introduced into the mouse embryonic stem cells
to silence one particular gene.
The altered cells are then introduced into early mouse embryos,
which are then implanted in a mouse womb.
The resulting pups have some tissues with altered genes,
but repeated breeding ensures mice that have all their tissues of the new type.
But very few genes have single effects
and altering one can have deadly consequences.
About 15% of mouse gene knockouts are lethal;
others produce unexpected handicaps.
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.