Clone is a transliteration of the English word "clone", which is generally translated as copy or transfer in Taiwan Province Province, Hongkong and Macau. It is a process of using biotechnology to produce offspring with the same genome as the original individual through asexual reproduction. Scientists call the process of artificial gene manipulating animal reproduction cloning, and this biotechnology is called cloning technology. Cloning technology itself is asexual reproduction, that is, a pure cell line formed by the division and reproduction of the same ancestor cells, in which each cell has the same genes.
Cloned English' clone' comes from the Greek' KL! N' (twig) In horticulture, the word "clone" was used until the 20th century. Later, sometimes' e' is added to the end of the word to become' clone' to indicate that' o' is pronounced as a long vowel. Recently, with the widespread use of this concept and word in public life, spelling has been limited to the use of "cloning". In Chinese mainland, the Chinese translation of this word is "clone", while in Hong Kong and Taiwan, it is usually translated as "clone" or "copy". The former "clone" is like the transliteration "copy" of copy, which has the disadvantage of not looking at the literal meaning; The latter's "copy" can roughly express the meaning of cloning, but it is not accurate and easy to be misunderstood.
Cloning is usually artificially induced asexual reproduction or natural asexual reproduction (such as plants). Cloning is a multicellular organism, genetically identical to another organism. Clones can be natural clones, such as asexual reproduction or individuals with identical genes (just like identical twins). But what we usually mean by cloning is an identical copy produced by conscious design.
Cloning technology is called "biological amplification technology" in modern biology. It has gone through three stages of development: the first stage is microbial cloning, that is, a bacterium quickly replicates thousands of identical bacteria and becomes bacterial colonies; The second period is biotechnology cloning, such as using genetic gene-DNA cloning; The third period is animal cloning, that is, cloning a cell into an animal. Dolly the cloned sheep was cloned from the somatic cells of ewe by animal cloning technology.
In biology, cloning is usually used in two aspects: cloning a gene or cloning a species. Cloning a gene refers to obtaining a gene from an individual (for example, by PCR) and then inserting it into it. In addition, there are also asexual reproduction in the animal kingdom, but it is more common in invertebrates, such as the division and reproduction of protozoa and the budding and reproduction of caudate animals. But for advanced animals, under natural conditions, they can only reproduce sexually, so scientists must go through a series of complicated operating procedures to make them reproduce asexually. In 1950s, scientists successfully cloned an amphibian, Xenopus laevis, which opened a new chapter in cell biology.
In the late 1980s, Britain and China successively used embryonic cells as donors to "clone" mammals. By the mid-1990s, China had cloned five kinds of mammals, including mice, rabbits, goats, cows and pigs.
19 Dragon produced Dolly, a lamb with the same genetic structure as the donor, which caused an uproar in the world. Dolly is special in that its life was born without the participation of sperm. The researchers first sucked genetic material from a sheep's egg cell and turned it into an empty shell, then took out breast cells from a 6-year-old ewe and injected genetic material into the empty shell of the egg cell. In this way, an egg cell containing new genetic material but not refined was obtained. This modified egg cell divides and proliferates to form an embryo, which is then implanted into the uterus of another ewe. With the smooth delivery of ewes, "Dolly" came into this world.
But why don't other cloned animals have such great influence in the world? This is because the genetic genes of other cloned animals come from embryos, and they are all nuclear transplants with embryonic cells, which cannot be strictly said to be "asexual reproduction". Another reason is that the embryonic cell itself is sexually propagated, and the genome in its nucleus is half from the father and half from the mother. Dolly's genome is all from a single parent, which is really asexual reproduction. Therefore, strictly speaking, "Dolly" is the first truly cloned mammal in the world. 1On February 23rd, 997, scientists from Roslin Institute in Scotland, England, announced that the successful use of goat somatic cell "cloning" technology by their research team was the result of scientific development, and it had a very broad application prospect. In horticulture and animal husbandry, cloning technology is an ideal means to cultivate varieties with stable genetic traits, and high-quality fruit trees and improved livestock can be cultivated through cloning technology. In the medical field, the United States, Switzerland and other countries have been able to use "cloning" technology to cultivate human skin for skin grafting. This new achievement avoids the possible rejection of allogeneic transplantation and brings good news to patients. According to China Xinhua News Agency1April 4, 1997, Cao Yilin, an expert in plastic surgery in Shanghai Ninth Staff Hospital, successfully cloned human ears in mice for the first time in the world, bringing hope for the repair and reconstruction of missing organs. Cloning technology can also be used to breed many valuable genes, such as insulin for treating diabetes, growth hormone that is expected to make dwarfism patients grow taller again, and interferon that can resist many diseases and infections.
Cloning is a major technological breakthrough in the field of biological sciences, which reflects the progress of nuclear differentiation technology, cell culture and control technology. Originally, it was a transliteration of English clone, which means the offspring individual population with the same genotype formed by biological cell asexual reproduction, referred to as "asexual reproduction". The great breakthrough of animal cloning technology has also brought widespread controversy.
The word "cloning" was introduced into horticulture in 1903, and gradually applied to botany, zoology and medicine. Broadly speaking, "cloning" is actually something we often encounter in our daily life, but it is not called "cloning". In nature, many plants have innate cloning instinct, such as sweet potatoes, potatoes, roses and other cutting propagation plants. However, animal cloning technology has experienced the development process from embryonic cells to somatic cells.
In spring, the 6-year-old ewe has exactly the same gene, which can be described as a copy of her mother. It is worth noting that cloning technology will not only bring great benefits to mankind, but also bring disasters and problems to mankind. However, we can't stop its development, because it may bring serious consequences. In the final analysis, its advantages outweigh its disadvantages, and it will be beneficial to the wide application of human beings. Individuals (usually through carriers) then study or use it. Cloning sometimes refers to successfully identifying a certain -{A|zh-cn: phenotype; Zh-tw: dominant gene. So when a biologist says that the gene of a disease has been cloned successfully, that is to say, the position and DNA sequence of this gene have been determined. Obtaining a copy of this gene can be considered as a by-product of identifying this gene.
Cloning an organism means creating a new object with exactly the same genetic information as the original organism. Under the background of modern biology, this usually includes somatic cell nuclear transfer. In somatic cell nuclear transfer, the nucleus of oocytes is removed and replaced by the nucleus taken from cloned organisms. Usually, oocytes and their transplanted nuclei should come from the same species. Because the nucleus contains almost all the genetic information of life, the host oocyte will develop into an organism genetically the same as the nuclear donor. Although mitochondrial DNA has not been transplanted here, it is still relatively rare, and its impact on organisms can usually be ignored.
In horticulture, cloning refers to the offspring of a single plant produced by vegetative propagation. Many plants obtain a large number of offspring from one plant by cloning this asexual reproduction.
Cloning technology can play a role in saving rare and endangered animals, expanding and improving animal populations, providing enough experimental animals, promoting the research of transgenic animals, overcoming hereditary diseases, developing high-level new drugs and producing internal organs for human transplantation, but if it is applied to human reproduction, it will produce a huge ethical crisis.
2 the development process of cloning technology
Early research on cloning
The genetic composition of all members of the same clone is exactly the same, unless there is mutation. Cloning of natural plants, animals and microorganisms has long existed in nature. For example, identical twins are actually clones. However, natural mammals have a very low incidence of cloning, a small number of members (generally two), lack of purpose, and are rarely used to benefit mankind. Therefore, people began to explore artificial methods to produce higher animal clones. In this way, the word cloning began to be used as a verb to refer to the behavior of artificially cultivating cloned animals.
At present, there are two main methods to produce mammalian clones: embryo segmentation and nuclear transfer. Dolly, a cloned sheep cultivated by scientists from various countries, and various cloned animals later adopted nuclear transplantation technology. The so-called nuclear transfer refers to the process of transplanting the nuclei of embryos or adult animals at different development stages into enucleated oocytes through microsurgery and cell fusion, re-forming embryos and making them mature. Different from embryo segmentation technology, nuclear transfer technology, especially continuous nuclear transfer technology, can produce an infinite number of genetically identical individuals. Because nuclear transfer is an effective method to produce cloned animals, people usually call it animal cloning technology.
The idea of cloning animals by nuclear transplantation was first put forward by Hans Spearman in 1938. He called it a "strange experiment", that is, taking out the nucleus from a developing embryo (mature or immature embryo) and transplanting it into an egg. This idea is the basic way to clone animals now.
Starting from 1952, scientists first carried out nuclear transfer cloning experiments with frogs, and successively obtained tadpoles and adult frogs. From 65438 to 0963, the scientific research group led by Professor Tong Dizhou in China studied the nuclear transfer technology of fish embryos for the first time, and achieved success. 1964, British scientist J.Gurdon irradiated the unfertilized eggs of Xenopus laevis with ultraviolet rays to destroy their nuclei, and then absorbed the nuclei from the wild epithelial cells, that is, the somatic cells of tadpoles, and injected them into the eggs whose nuclei were destroyed. The results showed that 1.5% of the transferred eggs differentiated and developed into normal adult frogs. Gordon's experiment proved for the first time that the somatic nuclei of animals are comprehensive.
The first achievement of mammalian embryo nuclear transfer research was obtained in 198 1 year-Karl Ilmen Ze and Peter Hope used mouse embryonic cells to culture normal mice. 1984, Steen Willadsen cloned a live-born sheep with immature embryo cells from sheep. Later, some people repeated his experimental method with various animals such as cattle, pigs, goats, rabbits and macaques. 1989, Willadson obtained the second generation of cloned cattle with continuous nuclear transfer. In 1994, Neil Fierst cloned a cow from a late embryo with at least 120 cells. By 1995, nuclear transfer of major mammalian embryos was successful, including frozen and in vitro embryos; Nuclear transplantation experiments of embryonic stem cells or adult stem cells have also been tried. However, until 1995, the transfer of differentiated nuclei in adult animals has not been successful.
The Significance and Response of Dolly the Cloned Sheep
What ethical principles did human cloning violate?
Human cloning violates human bioethics.
Should modern science and technology, especially modern life science and technology, respect ethical principles and listen to ethical voices? According to some scientific lunatics secretly cloning human beings in the United States, experts point out that cloning human beings violates human bioethics, and there are great controversies and a series of legal problems that are difficult to solve.
Recently, many domestic media reprinted an amazing news reported by foreign media: a group of scientific lunatics manipulated by cult organizations are conducting a secret human cloning experiment in the depths of the desert in Nevada, USA. According to the same principle that British scientists created Dolly, the world's first cloned sheep, they extracted cells from an American baby girl who died in February this year, and made clones. It is said that "if all goes well, the world's first clone will be born at the end of next year."
After the news was disclosed, cloning technology and its ethical issues once again became a hot topic of discussion. If this news is true, how to treat this matter and how to correctly evaluate and think about this issue, the reporter visited the director of the Ethics, Law and Society Department of the Southern Research Center of the National Human Genome and researcher Shen Mingxian of the Institute of Philosophy of the Shanghai Academy of Social Sciences. Professor Shen said: Since Dolly sheep was successfully cloned by Roslin Institute in England in 1997, driven by fame and fortune, people abroad have been proposing and trying to engage in human cloning research. Although governments have banned it, reports related to human cloning have appeared in newspapers more than once in the past two years. However, it is really shocking that this time the speed is so fast and it is related to cult organizations.
It is understandable that parents who have lost their beloved daughter hope to revive their daughter through cloning technology. But if scientists use this to carry out experiments on human cloning, it is worth discussing. Professor Shen believes that even if cults are abandoned, this practice is not desirable. As far as "human cloning" is concerned, he will live in the shadow of "I am a replica of the dead". How will this affect his psychology?
According to the viewpoint of bioethics, science and technology should proceed from long-term interests and benefit all mankind. It must follow the four internationally recognized ethical principles of "doing good, not hurting, independence and justice". Dolly's sheep cloning has successfully experienced more than 200 failures, and there have been deformed or aborted sheep. However, human cloning is more complicated and will undoubtedly encounter more failures. If we create unhealthy, deformed or short-lived people, it will be a violation of human rights.
Professor Shen pointed out that at present, the scientific community divides cloning into therapeutic cloning and reproductive cloning. The former uses embryonic stem cells to clone human organs for medical research to solve the problem of insufficient donors for organ transplantation, which is supported by the international scientific and ethical circles, but there is a premise that the embryos used for therapeutic cloning cannot exceed the limit of pregnancy 14 days. As for reproductive cloning, that is, human cloning, on the whole, it violates the principles of bioethics, so the mainstream opinion of scientists is firmly opposed. UNESCO, the World Health Organization, the International Human Genome Ethics Committee and governments all expressed their opposition to reproductive cloning very clearly. Even if human cloning is really born, we still have to stick to this basic position.
What is the trend of cloning technology?
Application prospect of cloning technology
Cloning technology has shown broad application prospects, which can be summarized as the following four aspects:
(1) Cultivate excellent varieties and produce experimental animals;
(2) producing transgenic animals;
(3) producing human embryonic stem cells for cell and tissue replacement therapy;
(4) reproduction of endangered animal species, preservation and dissemination of animal species resources.
The production of transgenic animals and embryonic stem cells is briefly described as follows.
The research on transgenic animals is one of the most attractive and promising topics in the field of animal bioengineering. Transgenic animals can be used as donors for medical organ transplantation, as bioreactors, as well as for genetic improvement of livestock and the establishment of experimental models of diseases. However, there are not many practical applications of transgenic animals at present. In addition to the medical model of transgenic mice modified by a single gene, the research on the production of drug proteins by mammary gland bioreactor of transgenic animals has been going on for a long time, which has been more than 10 years. But at present, only two drugs in the world have entered the phase III clinical trial, and 5 ~ 6 drugs have entered the phase II clinical trial. However, transgenic livestock strains whose agronomic traits have been improved and can be used for livestock production have not yet been born. The low production efficiency of transgenic animals, the high cost and regulation failure caused by the difficulty of fixed-point integration, and the separation of genetic characters of sexually propagated offspring of transgenic animals, which are difficult to maintain the excellent victory of ancestors, are the main reasons that restrict the practical process of transgenic animals today.
The success of somatic cell cloning has set off a new revolution for the production of transgenic animals, and animal somatic cell cloning technology provides a technical possibility for rapidly amplifying the germplasm innovation effect produced by transgenic animals. Using simple somatic cell transfection technology to transfer the target gene can avoid the difficulty and inefficiency of livestock germ cells. At the same time, the transgenic cell line can be used for pre-inspection of transgenic integration and gender pre-selection under laboratory conditions. Before nuclear transfer, the fusion gene of target exogenous gene and marker gene (such as LagZ gene and neomycin antibiotic gene) was introduced into cultured somatic cells, and then transgenic positive cells and their clones were screened through the expression of marker genes, and then the nucleus of the positive cells was transplanted into enucleated oocytes. Theoretically, the final animal should be a 100% positive transgenic animal. By this method, Schnieke et al. (Bio Report, 1997) have successfully obtained 6 transgenic sheep, of which 3 have human coagulation factor IX gene and marker gene (neomycin resistance gene), and 3 have marker gene, and the integration rate of target foreign gene is as high as 50%. Cibelli (Science, 1997) also obtained three transgenic cows by nuclear transfer, which confirmed the effectiveness of this method. It can be seen that one of the most important application directions of animal cloning technology today is to develop transgenic cloned animals with high added value.
Embryonic stem cells are totipotent stem cells and have the potential to form all adult cell types. Scientists have been trying to induce various stem cells to differentiate into specific tissue types to replace those damaged tissues in the body, such as implanting insulin-producing cells into diabetic patients. Scientists have been able to transform pig es cells into beating cardiac myocytes, human ES cells into nerve cells and mesenchymal cells, and mouse ES cells into endodermal cells. These results open the way for cell and tissue replacement therapy. At present, scientists have successfully isolated human es cells (Thomson et al. 1998, Science), and somatic cell cloning technology provides the possibility for producing patients' own ES cells. The patient's somatic cells were transplanted into enucleated oocytes to form recombinant embryos, which were cultured into blastocysts in vitro. Then es cells were isolated from blastocysts and differentiated into specific cell types (such as nerve cells, muscle cells and blood cells) for replacement therapy. The ultimate goal of this nuclear transplantation method is to treat stem cells, not to obtain cloned individuals, which scientists call "therapeutic cloning".
The application of cloning technology in basic research is also very significant, which provides a tool for studying the mechanisms of gamete and embryogenesis, cell and tissue differentiation, gene expression regulation, nuclear-cytoplasmic interaction and so on.
As a new research team, 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 success rates of cloning fetal fibroblasts and embryonic cells were only 65438 0.7% and 65438+, respectively.
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, saying that the British government would reconsider this decision and thought it unwise to ban this research blindly. The key is to establish certain norms and use them to benefit mankind.
A bacterium can split in two after about 20 minutes; A grape branch cut into ten segments may become ten grapes; Cactus is cut into several pieces, and each piece takes root when it hits the ground; A strawberry can grow hundreds of strawberry seedlings a year by its creeping stolon on the ground ... These are all creatures that reproduce their offspring by splitting themselves in two or expanding a small part of themselves. This is called asexual reproduction. The English name of asexual reproduction is "Clone", transliterated as "clone".
Many animals in nature, under normal circumstances, rely on male cells (sperm) produced by their fathers and female cells (eggs) produced by their mothers to fuse (fertilize) into fertilized eggs (zygotes), and then the fertilized eggs develop into embryos through a series of cell division, and finally form new individuals. This kind of reproduction mode, which relies on the sex cells provided by both parents and produces offspring through the fusion of bisexual cells, is called sexual reproduction. However, if we divide the embryo into two parts, four parts and eight parts through surgery ... finally, an embryo grows into two, four and eight ... organisms through special methods. These creatures are cloned individuals, and these two, four, eight ... individuals are called clones (also known as clones).
1In the spring of 979, scientists from Wuhan Institute of Hydrobiology, Chinese Academy of Sciences artificially cultured the cells in the blastocyst stage of crucian carp. After 59 generations of continuous subculture for 385 days, the nucleus was sucked out of the cultured cells by a glass tube with a diameter of about 65438 00 microns under a microscope. At the same time, the nucleus of crucian carp eggs was removed to prepare the eggs for accepting blastocyst nuclei. After everything is ready, the nucleus sucked out of the glass tube is moved into the empty position of crucian carp eggs, and most of the blastocyst nuclei under artificial culture die prematurely. Of the 189 eggs exchanged by nuclear exchange, only two hatched fry, and finally only one young fish survived the difficulties. After more than 80 days of culture, it grew into a crucian carp with a body length of 8 cm. This kind of crucian carp has not been combined with male and female cells, but only replaced the nucleus of a blastocyst with an egg cell, which is actually produced by the egg after nuclear replacement, so it is also a cloned fish.
Before the emergence of cloned crucian carp, scientists from Oxford University in England had conducted cloning experiments with a Xenopus laevis (Xenopus laevis) in 1960 and 1962. The experimental method is to irradiate Xenopus laevis eggs with ultraviolet rays to destroy their nuclei, and then take out the nuclei from the intestinal epithelial cells, liver cells and kidney cells of Xenopus laevis tadpoles through superb surgery, and accurately put the nuclei of these cells into the eggs whose nuclei have been destroyed by ultraviolet rays. After careful care, some of these nuclear exchange eggs finally grew up alive and kicking Xenopus laevis, which was not produced by the combination of sperm cells and egg cells, so it was also a cloned Xenopus laevis.
Tong Dizhou, a famous biologist in China, successfully conducted the cloning experiment of Rana nigromaculata in 1978. He transplanted the red cell nucleus of Rana nigromaculata into the eggs of Rana nigromaculata which had been enucleated in advance, and the eggs after enucleation eventually grew into tadpoles that could swim freely in the water.
With the maturity of fish nuclear exchange technology and the success of amphibian nuclear exchange, a group of scientists engaged in seed cultivation are excited. Since the nucleus of crucian carp blastocysts can replace the nucleus of crucian carp eggs to obtain cloned fish, can the nuclear exchange of heterogeneous fish get new hybrid fish? Scientists in China first proposed and solved this problem, that is, the research institute that successfully cultivated cloned crucian carp managed to replace the nucleus of crucian carp embryo cells with the nucleus of crucian carp egg cells. The nucleus of carp and the cytoplasm of crucian carp eggs can coexist peacefully and begin a process similar to the division and development of fertilized eggs. Finally, a kind of "crucian carp" with a beard grows very fast, just like carp, but its lateral scales and spines are the same as those of crucian carp, and the taste of fish is no less than that of crucian carp. The emergence of this new species of artificially cloned fish has opened up a new way for fish breeding.
The pursuit of science is endless, and the success of fish and amphibian cloning naturally makes scientists turn their attention to mammals. Scientists in the United States and Switzerland took the lead in taking out the nucleus from the embryonic cells of gray mice and replacing the nucleus of fertilized eggs of black mice with this nucleus. In fact, the fertilized egg of this black mouse just entered the egg cell and removed the sperm nucleus together with the egg nucleus. After transplanting the embryo nucleus of squirrel into the enucleated fertilized egg of a black mouse, it was artificially cultured in a test tube for four days and then implanted into the uterus of a white mouse. After hundreds of gray, black and white operations, the white mouse finally gave birth to three little squirrels.
The British journal Nature 1996 published on February 27th published the research results of wilmot and others of Roslin Institute in Edinburgh: After 247 failures, they got a cloned ewe named Dolly in July the year before last.
How was Dolly the Sheep "created"? Wilmot and other scholars first injected gonadotropin into Scottish black-faced sheep to induce ovulation. After getting the egg, they immediately took out the nucleus from the egg cell with a very thin straw. At the same time, they took out the nucleus from the mammary gland cells of a six-year-old ewe named Fendosit, who was pregnant for three months, and immediately sent it to the egg cells of the enucleated Scottish black-faced sheep. After the operation, they used electric pulses with the same frequency to stimulate egg exchange. Let the cytoplasm of Scottish black-faced sheep and the nucleus of breast cells of FenDorset ewe coordinate with each other, let this "assembled" cell undergo the process of division and development like a fertilized egg in a test tube, form an embryo, and then skillfully implant the embryo into the uterus of another ewe. In July last year, the ewe that "nursed" the embryo in vitro finally gave birth to Dolly, a lamb. Dolly is not the product of fertilization between ewe eggs and ram sperm cells, but the result of the step-by-step development of "nuclear-egg exchange", so it is "cloned sheep"
The birth of "cloned sheep" shocked all countries in the world. Its commendable feature is that it is the nucleus of somatic cells, not the nucleus of embryos. This result proves that the so-called highly differentiated cells that perform special functions and have specific forms in animals have the potential to develop into complete individuals like fertilized eggs. In other words, animal cells are totipotent like plant cells.
Cloning technology will bring great benefits to mankind. For example, the ewe bred by British PPL company contains a- 1 antitrypsin for treating emphysema. The price of this goat's milk is $6,000 a liter. A ewe is like a pharmaceutical factory. What is the most effective and convenient way to breed this kind of sheep? The best way is to "clone". Similarly, Dutch PHP company has bred cows that can secrete human lactoferrin, and Israeli LAS company has bred sheep that can produce serum albumin. How can these high value-added livestock breed effectively? The answer is of course "cloning".
A mare with a donkey can get an animal with particularly strong heterosis-mule. Mules can't reproduce, so how can excellent mules expand their reproduction? The best way is also "cloning". The giant panda in China is a national treasure, but its natural mating success rate is low and it is on the verge of extinction. How to save such rare animals? "Cloning" provides a practical way for human beings.
Cloning animals also plays an important role in studying cancer biology, immunology and human life span.
Undeniably, the appearance of "cloned sheep" has also aroused many people's interest in "human cloning". For example, some people are considering whether they can clone an embryo from their own cells and freeze it before it takes shape. One day in the future, when something goes wrong with one of our own organs, we can take this organ out of the embryo for culture and then replace our diseased organs, which is to provide ourselves with "accessories" through cloning.
The discussion about "human cloning" reminds people that scientific and technological progress is a mixed March. The more science and technology develop, the wider and deeper it penetrates into society, and the more likely it is to cause many related ethical, moral and legal problems. I want to end this article with a sentence from J.D. Watson, a famous molecular biologist who won the Nobel Prize: "It can be expected that many biologists, especially those engaged in asexual reproduction research, will seriously consider its significance and start scientific discussions to educate people all over the world."