柯灵思英语-英语听力高手38
Since early 1990s，we have used artificial insemination to increase the number of pandas，cloning pandas，controlling the female's heat and ovulation periods by injecting hormones，then putting the male's sperm 1 into it，thus resulting in a new being.
In the past six years，the method has produced six twins and seven single babies.
But the method of artificial insemination is still far from satisfactory with regard to the fate of the whole family. Moreover，because pandas usually produce only a small number of eggs and sperms，and when the female panda can't take part in the mating, the method won't work.
In 1997, the more ambitious plan-to clone the panda started. The experiment aims to implant 2 a nucleolus of a panda's body cell into a denucleated ovum, thus producing a completely new being.
We are aware that deformity, stillbirth and early death are regular occurrences in cloned animals. Moreover, statistics show that the abnormal embryo 3 gene 4 occurs less than 1 percent to natural births, 15 percent to test-tube babies and 50 percent to cloned animals.
The true challenge is the second step of cloning a pandaproducing a new panda baby in the matrix of another kind of animals. At present, we're not sure which animal will be the ideal "surrogate mother". You may say that the rabbit should be the "mother", since the embryo was produced in the rabbit's ovum. However, the problem is that the rabbit's matrix is too small for a baby panda. In addition, the gestation 5 period of the panda is between 87 to 170 days, while for a rabbit, it is less than 30 days. How can a rabbit conceive a panda?
Even if a panda is cloned, it only has the DNA 6 of the panda that provided the body cell. Therefore, to a certain degree, cloning does nothing to protect the animals. If a baby panda lives with the "surrogate mother", say a dog or bear, and thus learns the mother's behavior and habits, it will simply become a dog or a bear with a panda's body. What, then, is the point of panda cloning?
In any case, panda cloning has attracted so much attention. We are ruthlessly faced with the hard fact that pandas have a very poor propagation capacity，thus bringing them to the brink 7 of extinction 8．Of course，panda cloning is by no means meant to replace natural propagation. Quite on the contrary，cloning is complementary to natural and artificial methods. Our position is that we will try the method of panda cloning as long as it is beneficial to the protection of pandas．
- Only one sperm fertilises an egg.只有一个精子使卵子受精。
- In human reproduction,one female egg is usually fertilized by one sperm.在人体生殖过程中，一个精子使一个卵子受精。
- A good teacher should implant high ideals in children.好教师应该把高尚理想灌输给孩子们。
- The operation to implant the artificial heart took two hours.人工心脏植入手术花费了两小时。
- They are engaging in an embryo research.他们正在进行一项胚胎研究。
- The project was barely in embryo.该计划只是个雏形。
- A single gene may have many effects.单一基因可能具有很多种效应。
- The targeting of gene therapy has been paid close attention.其中基因治疗的靶向性是值得密切关注的问题之一。
- The gestation period can be anything between 95 and 150 days.妊娠期从95天至150天不等。
- This film was two years in gestation.这部电影酝酿了两年。
- DNA is stored in the nucleus of a cell.脱氧核糖核酸储存于细胞的细胞核里。
- Gene mutations are alterations in the DNA code.基因突变是指DNA密码的改变。
- The tree grew on the brink of the cliff.那棵树生长在峭壁的边缘。
- The two countries were poised on the brink of war.这两个国家处于交战的边缘。
- The plant is now in danger of extinction.这种植物现在有绝种的危险。
- The island's way of life is doomed to extinction.这个岛上的生活方式注定要消失。