高中英语 Unit 2 Cloning What is cloning素材 新人教版选修8(1).doc

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 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 unfertilized egg from which the nucleus had been removed. 277 cells were fused in this way, resulting 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 cloned 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 2003 the first cloned mule 6, horse 7 and rat 8 were reported.animal welfarecloning 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 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 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 after 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.11cloning techniques also require a great deal 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 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 residual 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 the cause of long-term deleterious effects.12one 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 faster, 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, 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 driving 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. 13it is clear that cloning may cause a great deal of animal suffering. the so-called benefits,