Although cloning technology has broad application prospects, it is still far from industrialization. As a new research field, cloning technology is not mature in theory and technology. Theoretically, the mechanism of reprogramming genetic material through differentiated somatic cell cloning (the process in which all or most genes in the nucleus are turned off and cells regain totipotency) is still unclear. Whether cloned animals will remember the age of donor cells, whether the continuous offspring of cloned animals will accumulate mutant genes, and the genetic role played by cytoplasmic mitochondria in the cloning process have not been solved.

In practice, the success rate of cloning animals is still very low. In the experiment of cultivating Dolly, Wilmut's research team fused 277 eggs with the transplanted nucleus, and only one live sheep Dolly was obtained, with a success rate of only 0.36%. At the same time, the cloning success rates of embryonic fibroblasts and embryonic cells were only 65,438 0.7% and 65,438 0.5%, respectively. 36866.88868688666

In addition, some born individuals show physiological or immune defects. Taking cloned cattle as an example, many cloned cattle cultivated in Japan, France and other countries died within two months after birth; By February 2000, 12 1 somatic cloned cattle had been born in Japan, but only 64 cows survived. The results showed that the placental function of some calves was not perfect, and the oxygen content and growth factor concentration in blood were lower than the normal level. The thymus, spleen and lymph glands of some calves are abnormal; Fetuses of cloned animals generally tend to develop faster than ordinary animals, which may be the cause of death.

Even Dolly, who developed normally, was found to have signs of premature aging. The end of the chromosome is called telomere, which determines the number of times a cell can divide: every time it divides, the telomere will be shortened, and when the telomere is exhausted, the cell will lose its ability to divide. 1998, scientists found that Dolly's cell telomeres are shorter than those of normal people, that is, its cells are in a more aging state. At that time, it was thought that this might be caused by the cloning of Dolly from adult sheep cells, which made its cells bear the imprint of adult cells. However, this explanation is now questioned. Robert Lanza, a doctor in Massachusetts, USA, cloned cattle from cultured aging cells and got six calves. After 5 ~ 10 months of birth, it was found that the telomeres of these cloned cows were longer than those of ordinary calves of the same age, and some even longer than those of ordinary newborn calves. At present, it is not clear why this phenomenon is different from Dolly's. However, this experiment shows that in some cases, the cloning process can change the molecular clock of mature cells and make them "rejuvenate". The effect of this change on the life span of cloned animals needs further observation.

In addition to the above theoretical and technical obstacles, the ethical impact of cloning technology (especially its application in human embryos) and the strong public reaction to it also limit its application. However, the development of cloning technology in recent years shows that most countries in the world are unwilling to lag behind, and no one has given up the research on cloning technology. At this point, the attitude of the British government is very representative. Less than 1 month after the end of February 1997, the British Science and Technology Council published a special report on cloning technology, indicating that the British government would reconsider this decision and think it unwise to ban this research blindly. The key is to establish certain norms and use them to benefit mankind.