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Genetic Engineering
文/Christopher Barnatt
Genetic engineering is the science of altering living things by changing the information encoded in their deoxyribonucleic acid or "DNA". Genetic information is stored in DNA using four different chemicals called adenine, cytosine, guanine and thymine. Abbreviated to the letters "A", "C", "G", and "T", these base chemicals are coupled together to form the linkages or "base pairs" that hold together the two spirals that comprise every DNA molecule.
Any organism's entire genetic sequence is known as its "genome" and contains millions and often billions of DNA base pairs. For example, human DNA contains about three billion. However, rather than working with individual base pairs, genetic engineering is concerned with far larger DNA segments known as genes.
A Broad Church
Genetic engineering is a very broad discipline that is best broken down into its areas of practical application in order to be most easily understood. At the highest level, genetic engineering can be sub-divided into the creation of genetically modified (GM) plants, animals and micro-organisms, as well as the application of genetic engineering in healthcare, otherwise known as genetic medicine. In turn, genetic medicine may be usefully sub-divided into the fields of genetic testing, pharmacogenetics, and gene therapy.
GM Plants
All forms of genetic modification (GM) take one or more genes from one species and introduce it into the DNA of another in order to create a "transgenic" organism with different characteristics. So, for example, a plant may be made more resistant to disease, drought or pesticides by introducing a foreign gene from another species into its genome.
One of the first GM plants was created at the University of California in 1986. Here, some tobacco plants were transgenically altered with a gene from a firefly to make them bioluminescent. The result was GM tobacco capable of emitting a glow.
The first commercial GM plant was the Flavr Savr tomato. Created by Calgene, this was licensed for human consumption in 1994. Specifically, Calgene used "gene silencing" technology to shut down the gene that causes tomatoes to rot, so allowing the GM produce to stay firm for longer after harvest.
GM Animals
Transgenic animals have also already been created. Way back in 1986 the first transgenic mice were genetically altered to develop cancer. Since that time the creation of "humanised" transgenic mice and rats for research purposes has also almost become routine.
A new breed of "enviropig" has also now been transgenically created by the Guelph Transgenic Pig Research Program to produce a more environmentally-friendly form of manure. Back in 1996, the Roslin Institute in Scotland also successfully managed to clone a sheep called "Dolly" by transplanting an udder cell nucleus from one sheep into an empty egg cell from another. Since that time the same technique has been used to clone pigs, dogs and horses.
Today, we are on the brink of the approval of the first GM creature to enter the human food chain. Created by a company called Aqua Bounty Technologies, the AquAdvantage is a transgenic salmon that has had ocean pout and chinook salmon genes spliced into its DNA. The result is a fish that grows to full size in 18 rather than 36 months.
GM Micro-organisms
For centuries natural fermentation processes have been used to produce products including cheese, beer and yoghurt. However, since the birth of genetic engineering in the 1970s, genes have also been spliced between micro-organims in order to enable the creation of products using transgenic E.coli bacterium and other micro-organisms.Today, transgenic E.coli bacterium are used to produce all manner of things including chymosin (as required in the making of cheese), as well as synthetic insulin, human growth hormones, and first generation bioplastics and biofuels.
Genetic Testing
Ever since the completion of the Human Genome Project, hopes have been high for the application of genetic engineering in healthcare. While progress has been slower than the media anticipated -- and the role of most of the genes in human DNA is far from understood -- already more than 1,000 human genetic tests are available. These enable couples who conceive a child using in vitro fertilization (IVF) to have embryos screened for the genetic mutations that cause cystic fibrosis, sickle cell disease, spinal muscular atrophy, and a range of other conditions.
Major research is also underway into the genetics of cancer. For example the International Cancer Genome Consortium has been set up to generate genetic data on up to fifty of the most common types of cancer. In time, this work should allow doctors to test for and diagnose cancers based on their genetic characteristics. Further into the future, cancer gene therapies may also result.
Pharmacogenetics
Pharmacogenetics -- also known as pharmacogenomics -- is the study of how genes influence a person's response to drugs. It has always been obvious that different people respond differently to the same medication. However, it has usually not been known why. The promise of pharmacogenetics is to alter this situation by allowing doctors to select treatments based on the genetic makeup of each individual patient.
Pharmacogenetics will also allow prescriptions to be calculated based on a person's genetics rather than purely their weight and age. Vaccines will also be able to be genetically targeted, with different strains for different patient DNA profiles. In addition, pharmacogenetics will allow medicines that work very well in some people but cause major side effects in others to be safely brought to market as it will be known who will react badly to them and who will not.
Gene Therapy
The ultimate goal of genetic medicine is to cure health complaints at the genetic level. Potentially, several mechanisms exist that could be used to insert additional or replacement genes into a patient's DNA. These include the use of gene transfer agent viruses known as "vectors" to deliver therapeutic genes to target patient cells. Alternatively, therapeutic genes may be coated with artificial liposomes. These fatty substances adhere to the surface of cells and may therefore encourage attached genes to enter into them.
The World of the Designer Baby
Gene therapy and related genetic engineering research in human beings is currently tightly regulated (if to very different degrees in different parts of the world). However, we already live in the world of the designer baby, with IVF now widely used to help some couples conceive. Indeed, in the UK, about one child in fifty is now born as a result of IVF. Babies conceived via IVF are also routinely screened for genetic diseases. With certain embryos then consciously selected for implantation, human choices are thereby already being made regarding the characteristics of resultant children.
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基因工程
譯/上海譯銳翻譯全職B檔譯員 Jason MA
基因工程是一門通過改變生物體內脫氧核糖核酸（或DNA）中的編碼信息，進而使生物發生改變的學科。DNA通過四種不同的化學物質來儲存基因信息。這四種化學物質分別是腺嘌呤、胞(核)嘧啶、鳥嘌呤和胸腺嘧啶。這四種基礎化學物質（用字母“A”、“C”、“G”、“T”來表示）通過配對組合來形成堿基對。堿基對使每個DNA分子中都存在的雙螺旋體相結合。
所有生物的完整基因序列也叫做基因組。完整的基因序列的DNA堿基對達數百萬個以及數十億個，而數量在數十億的則更為常見。比如說，人類的DNA中就包含了大約30億個堿基對。不過，基因工程所研究的并非是單個的堿基對，而是要比堿基對大的多的DNA片段。這種DNA片段也被稱作基因。
一個廣泛的學科
基因工程是一門非常廣泛的學科。為了使其便于理解，這里最好按照不同的應用領域對其進行細分。處在最上端的基因工程可以被細分為培育轉基因植物、動物和微生物以及基因工程在醫療保健中的應用（亦被稱作基因藥物）。反過來，基因藥物可以被細分為基因測試、遺傳藥理學和基因治療。
轉基因植物
所有類型的轉基因都是將一個物種中的一個或幾個基因放入另外一個物種的DNA中，以培育出一種擁有不同特性的“轉基因”生物。因此，當一個植物內的基因組中包含了來自另外一個物種的基因，那么這個植物對于疾病、旱災或蟲害可能會擁有更強的抵抗力。
1986年，在首批出現的轉基因植物中，一種煙草轉基因植物在加利福尼亞大學誕生。在加利福尼亞大學，這種煙草植物被加入了螢火蟲的一個基因，以使其具有生物發光的特性。結果就是，這種轉基因的煙草植物能夠發光。
由Calgene公司所創造的“FLAVR SAVR”番茄是首個被商業化的轉基因植物。1994年，“FLAVR SAVR”番茄獲得許可，允許被人類食用。確切的說，Calgene公司通過利用“基因沉默”技術，關閉了導致番茄腐爛的基因，因此可以使番茄在采摘后擁有更長的保鮮期。
轉基因動物
轉基因動物也已經問世。早在1986年，第一批接受轉基因的老鼠的基因發生改變并因此而患上癌癥。從那時起，培育“具有人類特性”的轉基因小鼠和大鼠以用于研究幾乎已經成為慣例。
如今，一種新的轉基因豬已經誕生。這種由圭爾夫轉基因豬研究項目（Guelph Transgenic Pig Research Program）培育的新轉基因豬可以排出更加環保的糞便。1996年，位于蘇格蘭的Roslin研究院通過將一頭羊中的乳腺細胞核移植到另一頭羊的無核卵細胞中，成功克隆出一只綿羊。他們給這只綿羊取名為“多莉”（Dolly）。從那時起，人們開始使用同樣的技術來克隆豬、狗和馬。
今天，首批轉基因生物即將被允許出現在人類的食物鏈中。Aqua Bounty Technologies培育出一種被稱為AquAdvantage的轉基因三文魚。這種三文魚的DNA中被植入了大洋鱈魚和大鱗大馬哈魚的基因。新培育的轉基因三文魚僅需要18個月就可以發育成熟，而普通的三文魚則需要36個月。
轉基因微生物
幾百年來，人們一直使用天然的發酵工藝來制作奶酪、啤酒以及酸奶等食品。不過，自基因工程在20世紀70年代誕生以來，基因也開始被用于微生物之間的拼接，以利用轉基因大腸桿菌和其他微生物來制作食品。如今，轉基因大腸桿菌被用來生產各種包括凝乳酶（制作奶酪時需要）、人工合成胰島素、人生長激素以及第一代生物塑料和生物燃料在內的各種產品。
基因測試
自人類基因組計劃落幕后，人們對將基因工程應用于醫療保健領域一直抱有很高的期望。盡管進度比媒體所預想的慢一些，但目前已經有超過1000種針對人類基因檢測了。因此，采用體外受精的夫婦可以通過基因檢測對胚胎進行篩查，以排除能夠引起囊性纖維化、鐮狀細胞病、脊髓性肌肉萎縮癥和一系列其他病癥的基因突變。
有關癌癥遺傳學的主要研究也已經展開。例如，已經成立的國際癌癥基因組聯盟（International Cancer Genome Consortium）專門針對多達50種最常見的癌提供基因數據。屆時，這些數據可以幫助醫生根據癌的基因特性對其進行檢測和診斷。將來，癌癥基因療法可能也會應運而生。
藥物遺傳學
藥物遺傳學，也被稱作藥物基因組學是一項關于基因如何影響人類對藥物的反應的研究。不同的患者對同一種藥物會有不同的反應，這一點一直都是顯而易見的。不過，這其中的原因卻通常不為我們所知。藥物遺傳學有望改變這一局面，它能夠讓醫生根據每位患者的基因組成來選擇不同的治療方法。
藥物遺傳學還可以讓醫生根據患者的基因，而非僅根據患者的年齡和體重來配藥。疫苗也可以做到具有基因針對性，即根據患者的DNA圖譜來提供不同的菌株。此外，藥物遺傳學還可以讓對于某些患者具有顯著療效，而對于另外一些患者卻有明顯副作用的藥物能夠安全投向市場。因為，藥物遺傳學可以幫助我們知道哪些患者在服用這些要后會產生副作用，而哪些患者則不會。
基因治療
基因醫學的最終目的就是在基因層面使疾病得到根治。能采用的方法有好幾種，都是通過將額外或替代基因植入到患者的DNA中。具體包括使用基因轉移因子病毒，即“載體”來將治療基因送到患者的細胞中。另外一種方法是在治療基因的表面包裹一層人工脂質體。這些脂肪物質會粘附在細胞的表面，因此可能會促使所附帶的基因進入到細胞內部。
定制化的嬰兒
針對人類的基因療法和相關的基因工程研究目前受到嚴格的監管。盡管如此，隨著體外受精的廣泛應用，定制化的嬰兒已經到來。的確，在英國，借助體外受精而誕生的嬰兒與通過正常受精而孕育的嬰兒的比例為1：50。通過體外受精孕育的嬰兒也要進行常規的篩查，以排除遺傳性疾病。通過有意識的選擇要植入的胚胎，人類其實已經就未來一代的特性做出選擇了。