《高二英語(yǔ)（選修八）unit 2 備課參考 What is cloning》由會(huì)員分享，可在線閱讀，更多相關(guān)《高二英語(yǔ)（選修八）unit 2 備課參考 What is cloning（2頁(yè)珍藏版）》請(qǐng)?jiān)谘b配圖網(wǎng)上搜索。
1、
What is cloning?
Cloning means the production of genetically identical animals. In 1995 scientists at the Roslin Institute in Edinburgh, Scotland produced Megan and Morag - two lambs cloned from a single embryo. In 1996 Dolly the sheep was produced, the first example of a clone produced not from
2、an embryo cell but from a cell taken from an adult sheep. She was cloned using a nuclear transfer technique, where the nucleus from a cell taken from the mammary gland of an adult sheep was fused with an unfertilised egg from which the nucleus had been removed. 277 cells were fused in this way, resu
3、lting in 29 viable embryos which were implanted into surrogate Blackface ewes. One gave birth to Dolly. Dolly died in 2003 after suffering the signs of premature ageing such as arthritis and a liver complaint.
The 'production' of Dolly has sparked a cloning frenzy. 1998 saw the arrival of cows clon
4、ed using the same technique that produced Megan and Morag 1. The Roslin institute cloned the first pig in 2000 2. In the US in 2001 a rhesus macaque monkey called Tetra was cloned 3. Also in the US in 2002 a cloned kitten was reported 4 in the same year as the first cloned rabbits in France 5. In 20
5、03 the first cloned mule 6, horse 7 and rat 8 were reported.
Animal welfare
Cloning involves many possibilities for detrimental effects on animals. For example, cloned lambs and calves are frequently abnormally large at birth - some have been twice normal size. One cloning expert admitted in 1992
6、that "many cloned calves are abnormal".9 In Australia, a lamb of five times the mean birth weight for the breed has been recorded. In addition, cloned animals are often found to have malformed internal organs.10 Both of these adverse effects were seen in the first Edinburgh experiments in 1995 that
7、led to Megan and Morag. In addition to death through malformed internal organs, one lamb had to be delivered by caesarean section because it had grown to twice its normal size in the womb, and all but one of the five cloned lambs were at least 20% larger than they should have been.
Immediately afte
8、r birth many cloned lambs have breathing difficulties, are lethargic and often will not suckle. As a consequence, perinatal mortality is high. Miscarriage rates are also high; this is thought to be at least in part because of 'large offspring syndrome'.11
Cloning techniques also require a great dea
9、l of surgical intervention. Those sheep destined to be egg donors undergo hormone injections, followed by surgery to have the egg cells removed. Following nuclear transfer, it is common for the cloned embryos to be surgically implanted into temporary recipient sheep. Six days later, these temporary
10、'foster mothers' are simply killed and the embryos removed. The embryos are then placed, again surgically, into the surrogate mother ewes. Some deliveries have been achieved via Caesarean section. So the process is far from simple, and the surgery required can reasonably be expected to inflict resid
11、ual pain.
Attempts to create clones of animals that have been already cloned could also result in increased suffering. In France 1999, a calf which was a clone of a clone died aged eight weeks of rapid depletion of blood cells and severe anaemia. The researchers concluded "…somatic cloning may be t
12、he cause of long-term deleterious effects".12
One possible application of cloning, suggested by the Roslin team, is the facilitation of farm animal genetic engineering. If successful, the cloning technique could be used to 'mass produce' farm animals which had been genetically engineered to grow fa
13、ster, bigger or leaner. Cloning could also be used to mass produce animals genetically engineered to produce pharmaceutical proteins in their milk or blood (gene pharming), or for use in xenotransplantation. However, genetic engineering itself has a very poor track record in terms of animal welfare,
14、 and the BUAV is appalled at the idea of combining genetic engineering and cloning techniques.
Former Archbishop John Habgood has written of the motives behind cloning experiments:
"But should science be going down this road at all? What is the point of it? The simple answer is - money. The drivin
15、g force behind most of the research in this field has come from the agricultural industry. I use the word industry deliberately. Cloning is a means of standardising products, and that is what industry always wants." 13
It is clear that cloning may cause a great deal of animal suffering. The so-called 'benefits', such as the production of genetically identical herds or flocks of animals for intensive farming, may be seen as dubious or even highly unethical. The BUAV therefore believes that the practice of cloning should be stopped immediately.
單位：湖北省荊門(mén)市 姓名：李國(guó) E_mail：liguo619@
高二英語(yǔ)（選修八）unit 2 備課參考 What is cloning
