Cloning is the phonetic translation of English clone, which is simply a form of artificially induced asexual reproduction. But cloning is different from asexual reproduction. Asexual reproduction refers to the reproduction of offspring from a single organism without the union of male and female reproductive cells, commonly known as sporulation, budding and schizogamy. Asexual reproduction is the production of new individuals from plant roots, stems, leaves, etc. by pressing or grafting. Animals such as sheep, monkeys and cows cannot reproduce asexually without artificial manipulation. Scientists call the process of artificial genetic manipulation of animal reproduction cloning, and this biotechnology is called cloning.
The basic process of cloning is to transplant the nucleus of a donor cell containing genetic material into an egg cell whose nucleus has been removed, stimulate it with microcurrent to fuse the two into a single unit, and then cause the new cell to divide and multiply to develop into an embryo. When the embryo has developed to a certain extent, it is implanted into the animal's uterus to make the animal pregnant, and then the animal can be born with the same genes as those who supplied the cell. If the donor cells are genetically modified during this process, the offspring of the asexually reproduced animal will be genetically identical.
Cloning does not require the mating of a male and female or the union of a sperm and an egg, but only a single cell from an animal, which is artificially cultured into an embryo, which is then implanted into a female animal to give birth to a new individual. The cloned animal cultured from a single cell has exactly the same characteristics as the single-cell donor, and is a "copy" of the single-cell donor. Scientists in England (UK) and Oregon (USA) have produced "cloned sheep" and "cloned monkeys". The success of cloning technology has been called "a historic event, a scientific innovation". Some people even think that cloning technology can be compared with the introduction of the atomic bomb.
Cloning technology can be used to produce "clones", can be used to "copy" the human being, and therefore attracted widespread attention around the world. For human beings, cloning technology is sad or happy, is it a curse or a blessing? According to material dialectics, everything in the world is a unity of contradictions and is divided into two. This is also true of cloning technology. If cloning technology is used to "copy" war-mongers like Hitler, what will it bring to human society? Even if it is used to "clone" ordinary people, it will bring about a series of ethical and moral problems. If cloning technology is applied to livestock production, it will bring about a fundamental change in the breeding and reproduction of good livestock breeds. If cloning technology is used in gene therapy research, it is very likely to overcome the cancer, AIDS and other stubborn diseases that jeopardize human life and health. Cloning technology, like atomic energy technology, is a double-edged sword, the handle of which is in the hands of mankind. Humanity should take joint action to avoid the emergence of "clones", so that cloning technology to benefit human society.
Research on cloning technology
I. Early research on cloning
The word "clone" is the phonetic translation of the English word "clone", and as a noun, "clone" is usually translated as "asexual reproduction". The genetic makeup of all members of the same clone is identical, with exceptions only when mutations occur. Natural clones of plants, animals and microorganisms have long existed in nature, e.g., identical twins are actually a type of clone. However, since natural mammalian clones are so infrequent, have so few members (typically two), and lack purpose that they can rarely be used for human benefit, artificial methods of producing higher animal clones have been explored. In this way, the word clone began to be used as a verb to refer to the action of artificially breeding cloned animals.
At present, the two main methods of producing mammalian clones are embryo splitting and cell nuclear transfer. The cloned sheep "Dolly", as well as a variety of cloned animals bred by scientists in various countries since then, have adopted the cell nuclear transplantation technology. The so-called cell nuclear transplantation refers to the process of transplanting the nuclei of embryos or adult animals of different developmental periods into denucleated oocytes through microsurgery and cell fusion, so as to reorganize the embryo and make it mature. Unlike embryo splitting, nucleus transplantation, especially serial nucleus transplantation, can produce an unlimited number of genetically identical individuals. Because cell nuclear transplantation is an effective method of producing cloned animals, it is often referred to as animal cloning technology.
The idea of animal cloning by nucleus transplantation was first proposed in 1938 by Hans Spemann, who called it a "strange experiment" in which the nucleus of a cell was removed from an embryo at a late stage of development (mature or immature embryo is acceptable) and transplanted into an egg. This idea is now the basic route to cloning animals.
From 1952, scientists first used frogs to carry out nuclear cell transplantation cloning experiments, and successively obtained tadpoles and adult frogs. 1963, China's scientific research group under the leadership of Prof. Tong Di Zhou, first to goldfish and other materials, research on fish embryo nuclear cell transplantation technology, and achieved success.
The first results of mammalian embryonic cell nuclear transplantation research in 1981 - Karl Ilmenzer and Peter Hoppe with mouse embryonic cells to breed a normal development of mice. 1984, Sten Veladsen with immature embryonic cells taken from sheep cloned a live birth of sheep, and others later replicated the experimental methods he employed using a variety of animals, including cows, pigs, goats, rabbits, and rhesus monkeys. in 1989, Villadsen obtained cloned cows with two consecutive nucleus removals. in 1994, Neil Feldstetter cloned cows from late-stage embryos that had developed to have at least 120 cells. By 1995, nuclear transfer of embryonic cells had been successful in all major mammals, including frozen and in vitro-produced embryos; experiments with nuclear transfer of embryonic stem cells or adult stem cells had also been attempted. However, nuclear transplantation of differentiated cells in adult animals has not been successful until 1995.
The significance of the cloned sheep "Dolly" and the repercussions
The above facts show that, in February 1997, Dr. Wilmut's scientific research group at the Roslin Institute in the United Kingdom announced that somatic cell cloning of the sheep "Dolly" cultivation success before In fact, the cloning of "Dolly" followed the entire process of embryonic cell nuclear transplantation in terms of nuclear transplantation technology, but this does not diminish the great significance of "Dolly" because it is the world's first animal born through somatic cell nuclear transplantation, which is a great breakthrough in the field of cloning technology. This is a huge breakthrough in cloning technology. This great progress means that: theoretically, it has been proved that, like plant cells, the nucleus of differentiated animal cells also has totipotency, and there is no irreversible change of the genetic material in the nucleus during the process of differentiation; practically, it has been proved that it is feasible to utilize somatic cells for animal cloning, and that there will be countless identical cells that can be used as the donor for nuclear transplantation, and a series of complex genetic manipulations can be carried out on the donor cells before fusing with the oocytes. These donor cells can be subjected to a series of complex genetic manipulations before fusion with the egg cell, thus providing an effective method for large-scale replication of superior animal breeds and production of transgenic animals.
Theoretically, using the same method, a human being could be reproduced as a "clone," which means that the idea of the authoritarian maniacs of science fiction cloning themselves is entirely possible. Therefore, the birth of "Dolly" in the world's scientific community, political and even religious circles have caused a strong reaction, and triggered a discussion of the moral issues derived from human cloning. Relevant people in governments and civil society have responded that human cloning is contrary to ethics and morality. Nevertheless, the great theoretical significance and practical value of cloning technology has prompted scientists to speed up the pace of research, so that the research and development of animal cloning technology has entered a climax.
Three important results of cloning research in the past three years
The birth of the cloned sheep "Dolly" set off a wave of cloning research all over the world, followed by a succession of reports about cloning animals. In March 1997, one month after the birth of "Dolly", scientists from the United States, Taiwan and Australia published news of their successful cloning of monkeys, pigs and cows respectively. However, they all used embryonic cells for cloning, the significance of which cannot be compared with that of "Dolly". In July of the same year, the Roslin Institute and PPL announced the cloning of the world's first transgenic sheep with human genes, Polly, from genetically modified fetal fibroblasts. This achievement demonstrates the great value of cloning technology in breeding transgenic animals.
In July 1998, Wakayama et al. of the University of Hawaii reported that 27 viable mice were cloned from mouse ovary cells, of which 7 were cloned again from cloned mice, which is the second batch of mammalian somatic cell nuclear transplantation progeny after "Polly". In addition, Wakayama et al. used a new, relatively simple and highly successful cloning technique, different from that of Dolly, which was named the "Honolulu Technique" after the location of the university.
Since then, scientists in the U.S., France, the Netherlands, and South Korea have reported successes in cloning cows from somatic cells; the enthusiasm of Japanese scientists has been particularly impressive, with the Tokyo University of Agriculture and Technology, Kinki University, the Livestock Improvement Organization, and local (Ishikawa, Oita, and Kagoshima prefectures, etc.) livestock testing facilities, as well as private companies (such as Yukihin Dairy, the largest milk commodity company in Japan) working from July 1998 to April 1999 on cloning cows from Somatic Cell Cloning. The results of cloning cows from ear and rump muscles, ovarian mound cells, and mammary gland cells extracted from colostrum have been reported by dairy companies such as Snow Seal Dairy, the largest dairy company in Japan. By the end of 1999, somatic cell cloning offspring of six types of cells - fetal fibroblasts, mammary gland cells, ovarian mound cells, oviduct/uterine epithelial cells, muscle cells, and ear skin cells - had been successfully born worldwide.
In June 2000, China's Northwest A&F University of Science and Technology using adult goat body cells cloned two "cloned goats", but one due to respiratory dysplasia and early death. According to reports, the cloning technology used for the research group's own research, and the cloning of "Dolly" technology is completely different, which shows that China's scientists have also mastered the cutting-edge technology of somatic cell cloning.
In the different species of cell nuclear transplantation experiments have also achieved some encouraging results, in January 1998, the United States, the University of Wisconsin-Madison scientists to the cow's egg as a receptor, the success of the cloning of pigs, cows, goats, mice and rhesus monkeys five kinds of mammal embryos, the results of this study show that a species of unfertilized eggs can be taken from a variety of animals with the combination of mature cell nuclei. Although these embryos were miscarried, it made a useful attempt to the possibility of heterologous cloning. 1999, the United States scientists used cattle eggs to clone the embryos of the rare animal Pan sheep; Chinese scientists also used rabbit eggs to clone the early embryos of the giant panda, these results show that cloning technology has the potential to become a new way to protect and save endangered animals.
Fourth, the application of cloning technology prospects
Cloning technology has demonstrated a broad application prospects, summarized roughly the following four aspects: (1) breeding of good livestock breeds and the production of experimental animals; (2) the production of genetically modified animals; (3) the production of human embryonic stem cells used in cellular and tissue replacement therapy; (4) copying of endangered species of animals, the preservation and dissemination of animal species resources. . The following is a brief description of the production of transgenic animals and embryonic stem cells.
Transgenic animal research is one of the most attractive and promising topics in the field of animal bioengineering, and transgenic animals can be used as donors for medical organ transplants, as bioreactors, as well as for the genetic improvement of livestock and the creation of experimental models of diseases. However, at present, the practical application of transgenic animals is not much, in addition to a single gene modification of transgenic mice medical model has been applied earlier, transgenic animal mammary gland bioreactor production of drug proteins in the research of a longer period of time, has been carried out for more than 10 years, but at present in the world only 2 cases of drugs into the phase 3 clinical trials, 5 to 6 drugs into the phase 2 clinical trials; and its agronomic traits have been improved, can be funded No transgenic livestock lines with improved agronomic traits that can be used in livestock production have been born so far. The low production efficiency of transgenic animals, the high cost and regulatory failure caused by the difficulty of fixed-point integration, as well as the separation of genetic traits in the sexually reproduced offspring of transgenic animals and the difficulty of maintaining the excellent traits of the originator are the main reasons restricting the process of the practical application of transgenic animals today.
The success of somatic cell cloning has set off a new revolution in the production of transgenic animals, and the technique of animal somatic cell cloning has provided a technical possibility for the rapid amplification of the germplasm innovation effect produced by transgenic animals. The use of simple somatic cell transfection technology to implement the transfer of target genes can avoid the difficulties and inefficiencies of livestock germ cell sources. At the same time, the use of transgenic somatic cell lines allows pre-testing for transgene integration and pre-selection for sex under laboratory conditions. Before nuclear transfer, the fusion gene of the target exogenous gene and marker genes (e.g., LagZ gene and neomycin resistance gene) is introduced into cultured somatic cells, and then the transgene-positive cells and their clones are screened by the performance of the marker genes, and then the nucleus of this positive cell is transplanted into denucleated oocytes, and the final animals produced should theoretically be 100% positive transgenic animals. Using this method, Schnieke et al. (Bio Report, 1997) have successfully obtained 6 transgenic sheep, of which 3 with the human coagulation factor IX gene and marker gene (neomycin resistance gene), and 3 with the marker gene, with the integration rate of the target exogenous gene as high as 50%.Cibelli (Science, 1997) has similarly obtained 3 transgenic cows by using nuclear transplantation, confirming the method. Cibelli (Science, 1997) also utilized the nuclear transfer method to obtain three transgenic cattle, confirming the effectiveness of the method. From this, we can see that one of the most important application directions of animal cloning technology today is the research and development of high value-added transgenic cloned animals.
Embryonic stem cells (ES) are totipotent stem cells with the potential to form all adult cell types. Scientists have been trying to induce targeted differentiation of various stem cells into specific tissue types to replace those damaged body tissues, such as implanting insulin-producing cells into diabetic patients. Scientists have been able to transform porcine ES cells into beating heart muscle cells, human ES cells into neuronal and mesenchymal cells and mouse ES cells into endodermal cells. These results open the way for cell and tissue replacement therapies. Currently, scientists have succeeded in isolating human ES cells (Thomson et al. 1998, Science), and somatic cell cloning techniques offer the possibility of producing a patient's own ES cells. The patient's somatic cells are transplanted into enucleated oocytes to form a recombinant embryo, the recombinant embryo is cultured in vitro to a blastocyst, from which ES cells are then isolated, and the ES cells obtained are made to differentiate directionally into the specific cell types required (e.g., nerve cells, muscle cells, and blood cells) for use in alternative therapies. The ultimate goal of this nuclear transfer method is to use the cells for stem cell therapy, not to obtain a cloned individual, which scientists call a "therapeutic clone.
The use of cloning in basic research is also of great interest, as it provides tools for studying mechanisms of gametogenesis and embryogenesis, cell and tissue differentiation, regulation of gene expression, and nucleoplasmic interactions.
V. Problems of cloning technology
Although cloning technology has a wide range of application prospects, it is still a long way from industrialization. Because as an emerging field of research, cloning technology is still very immature in theory and technology, in theory, differentiated somatic cell cloning on the genetic material reprogramming (all or most of the genes in the cell nucleus shut down, the process of cellular re-establishment of totipotency) of the mechanism is still not clear; cloned animals whether they will remember the age of the donor cells, the successive progeny of the cloned animal whether the accumulation of mutant genes, and in the cloning The genetic role played by cytoplasmic mitochondria during cloning is still unresolved.
In practice, the success rate of animal cloning is still very low, Wilmut's research group in the cultivation of "Dolly" experiments, the fusion of 277 transplanted nucleus of the oocyte, only to obtain "Dolly", a live lamb, the success rate of only 0.36%, while the simultaneous conduct of the "Dolly", the success rate of only 0.36%, the success rate of only 0.36%. The success rate was only 0.36%, and the success rates of the simultaneous cloning experiments of fetal fibroblasts and embryonic cells were only 1.7% and 1.1%, respectively, and the success rate was only a few percent even when using the "Honolulu" technique, which uses less differentiated oocytes as the nucleus donor.
In addition, some of the individuals born showed physiological or immune deficiencies. Taking cloned cattle as an example, many cloned cattle bred in Japan, France and other countries died within two months after birth; by February 2000, 121 somatic cell cloned cows had been **** born throughout Japan, but only 64 survived. Observations have shown that some calves' placentas are not functioning well, and their blood oxygen levels and growth factor concentrations are lower than normal; some calves' thymus, spleen, and lymph glands have not developed properly; and there is a general tendency for cloned animal fetuses to develop more rapidly than normal, all of which may have contributed to the deaths.
Even normally developing "Dolly" has been found to show signs of premature aging. In 1998, scientists found that the telomeres of Dolly's cells were shorter than normal, meaning the cells were in a more senescent state. At that time, it was thought that this might be caused by cloning "Dolly" with adult sheep cells, so that its cells have the imprint of adult cells, but this explanation is now being challenged, the United States of America, Massachusetts doctor Robert Lanza and other cultured senescent cell cloning cattle, to get six calves, 5 to 10 months after birth, found that these cloned cattle The telomeres of these cloned calves were found to be longer than those of ordinary calves of the same age, and some were even longer than those of ordinary newborn calves. It is not clear why this phenomenon is happening, or why it is so different from the case of Dolly. But the experiment suggests that in some cases the cloning process can alter the molecular clock of mature cells to "rejuvenate" them, and it remains to be seen how such changes affect the lifespan of cloned animals.
In addition to the above theoretical and technical obstacles, cloning technology (especially in the application of human embryos) on the ethical and moral impact and the public's strong reaction to this also limit the application of cloning technology. However, the development of cloning technology over the past few years has shown that all the major scientific and technological countries in the world are not willing to lag behind, and no one has given up the research on cloning technology. The attitude of the British Government is very representative. Less than a month after the announcement of the suspension of investment in the Dolly research team at the end of February 1997, the British Science and Technology Commission issued a special report on cloning technology, indicating that the British Government would reconsider its decision and that it would not be wise to prohibit research in this area blindly. The key is to establish certain norms to utilize it for the benefit of mankind.
Respondent: Governor ☆ Governor - Trial Level 3-7 20:59
I. The concept of cloning
It is well known that the reproduction of organisms is accomplished through reproduction. There are two ways of reproduction in living things: one is called sexual reproduction and the other is called asexual reproduction.
Sexual reproduction is reproduction through the fusion of reproductive cells (sperms and eggs) of both sexes and the development of offspring. Asexual reproduction does not involve the fusion of reproductive cells of the two sexes, but rather the division of the organism itself or the growth and development of its body cells to form an individual. Asexual reproduction is common in plants and some animals (e.g., unicellular animals and lower animals).
Clone is the phonetic translation of the English word "clone", which comes from the Greek word klon, originally meaning seedling or shoot, referring to asexual or nutritive reproduction of some plants. With the passage of time and the development of science, its meaning has increased a lot of content, such as a cell in vitro culture to produce a group of cells; by the "parent" sequence of DNA sequences and so on. In a nutshell, cloning is the process of obtaining a genetically identical group of cells or individuals through asexual reproduction from a single cell or individual.
The Monkey King in China's classic "Journey to the West" can "change" into many Monkey Kings by pulling out a handful of hairs and blowing on his breath. Because plucking a handful of hairs must bring down a group of cells, this group of cells will be able to cultivate a group of the same Sun Da Sheng. This also belongs to asexual reproduction. It is only that Sun Da Sheng is so powerful that he can "clone" a thousand of himself in an instant. In short, cloning is asexual reproduction, that is, "copy", "replica".
Second, the cloning of plants
Asexual reproduction ( cloning ) is originally a low-level reproduction. The lower the level of evolution of an organism, the more likely it is to adopt this mode of reproduction, and the higher the level of evolution, the less likely it is to adopt this mode of reproduction. Since low-level organisms, such as microorganisms, reproduce by dividing themselves into offspring that have exactly the same genetic material as their parents, microorganisms are not "individuals" in this sense, and they do not die. Although, in the strict sense, there are still some differences between the parents and the offspring of microorganisms, because there are still differences in their external nutrient environments, from the point of view of higher animals, such differences seem to be too insignificant. Under conditions where such differences are negligible, one could say that for microorganisms they are immortal. Death is a product of higher stages of biological evolution. Nowadays, in biomedical research, normal cells or cancer cells grown in vitro by cloning techniques are also called "immortal cell lines", meaning that these cells are "immortal".
Biomedical research into the microscopic level, the use of cloning technology to cultivate normal or abnormal cells of the immortal cell line, although it is a very difficult work, but has been in the scientific and medical communities in various countries more and more attention. In agriculture, people have long been using methods such as branching and pressing to propagate plants suitable for human needs. In animal husbandry, all countries are carrying out research on the use of cloning technology to produce more good breeding animals. But the development of an adult from the body cells of an adult higher organism is a major development in cloning technology.
Many years earlier, researchers at Cornell University in the United States stirred ripe carrots at high speed to obtain individual carrot cells, and then placed these individual cells in a growth medium to produce genetically identical carrots. This experiment confirmed the doctrine of plant cell totipotency. The doctrine of plant cell totipotency means that every cell of the plant body, including somatic cells, has the potential to develop into a complete individual.
The doctrine of plant cell totipotency has been widely proved in the plant world. Now we can any kind of living cell, tissue, or organ of the plant body, which has been artificially cultured in vitro to obtain its complete plant and produce many plants. This technique is known as tissue culture. It has been used for factory production of test tube seedlings of flowers, crops (like sugarcane).
Three, the course of animal cloning
Research on asexual reproduction in animals has been a subject of exploration for scientists. Because human beings have been selecting and breeding livestock breeds through the method of sexual reproduction for thousands of years, the result is the production of some excellent individuals or groups. They are more capable of meeting people's needs and wishes than ordinary individuals. For example, a cow with exceptionally high milk production, a flock of sheep with high wool production, a prize-winning racehorse or an excellent police dog. However, the performance of sexually reproduced offspring is not always the same as that of their parents, and some are even inferior to them. The reason for this is that the egg or sperm carries only any half of the alleles that make up the parent, and there can be almost infinite combinations of alleles, resulting in different offspring. Brothers, sisters, siblings, and siblings are all very different from each other because it is extremely difficult to have exactly the same genotype.
So it is very difficult to maintain an expression through sexual reproduction. It is obviously economically valuable to obtain a desirable phenotype, such as a cow with a high milk yield, and then to maintain, expand and reproduce that phenotype through asexual reproduction, i.e., to produce many genetically identical individuals.
Oocyte culture into adults
1951 ~ 1959, China's famous cell biologist Zhu Xian, etc., with a diameter of 10 ~ 13um glass needle stimulation to remove the egg membrane of the toad oocytes, the world's first culture of 25 toads into adults, i.e., no father toad. The longest of them could live up to 8 months.
Germ cells were used in these experiments. Can somatic cells be cultured to obtain an animal body? I.e., does the totipotency that plant cells have, do animal cells also have? There is no doubt that every animal cell, including somatic cells, has the full set of genes of the species, but direct culture of adult animals from somatic cells has not been successful so far. In order to prove that animal cells also have totipotency, biologists have conducted a large number of cell nuclear transplantation experiments.
Peak cell nuclear transplantation test
1939, scientists conducted the first nuclear transplantation test in amoebas. They moved nuclei into homologous enucleated amoebas, and as a result, the reconstituted amoebas could grow and reproduce offspring.
In 1963, China's famous biologists, such as Tong Di Zhou, conducted a large number of fish nuclear transplantation tests. In 1980, they will be carp blastocyst stage cell nucleus as the donor nucleus, crucian carp unfertilized nucleus mature egg cells as the acceptor mass, 2.7% of the nucleus transfer egg development to adult fish. The main traits of the carp transplants were the same as those of the carp, but the number of vertebrae was the same as that of the crucian carp, and the number of lateral scales was intermediate between the two species. This cell-engineered fish grows 22% faster than carp, and is now in production on a large scale.
In 1966, scientists used the amphibian African clawed toad to carry out nuclear transplantation experiments. They will be tadpole intestinal cells of the nucleus into the nucleated egg cells, the result is that 1.5% of the recombinant cells developed into a body. Their experiments demonstrated for the first time that animal somatic cells also have totipotency, but this has not yet been demonstrated in mammalian somatic cells.
Cloning mammals with embryonic cells
In 1986, British scientists used sheep's 8-cell embryonic cells ( in the 8-cell embryo before the cells can only show totipotency ) to do the nucleus cells, sheep's egg cells to do the plasmacytoid cells, the result of recombination cells can develop into sheep adult, and then successively with embryonic cells cloned cattle, mice, rabbits, monkeys and other animals. It should be noted that the test is not to replicate male or female sheep, but to replicate their offspring, so the test also has certain shortcomings or defects.
In China, the cloning of mammals with embryonic cells, the late 80s has been cloned free; 1991 Northwest Agricultural University and Jiangsu Agricultural College cloned sheep; 1993 Institute of Development of the Chinese Academy of Sciences and Yangzhou University College of Agriculture cloned goats; 1995 South China Normal University and Guangxi Agricultural University cloned cattle. In addition, the Hunan Medical College also cloned rats. However, the cloning of mammals from somatic cells other than embryonic cells was pioneered by British scientist Wilmut.
Four, the birth of "Dolly"
"Dolly" is the world's first case of somatic cells - mammary epithelial cells, through the cell nuclear transplantation technology, under the complex manual operation, to obtain The procedure is as follows. The operation process is like this:
Closer from the Scottish black-faced ewes ( a sheep ) out of the eggs, and the genetic material of the eggs sucked, become only cytoplasmic eggs.
Peake from the second trimester of pregnancy ewes ( B sheep ) removed mammary epithelial cells, in vitro passaging culture for 3 - 6 generations, and drug treatment to control the development of the cells in the resting phase. This is a very critical step. The resting cells were then used as donor cells.
3 A donor cell is introduced into the inner lumen of the zona pellucida of the above mentioned egg. It is then stimulated with electrical pulses to fuse the donor cell with the egg to form a reconstituted egg.
Sung the reconstructed egg into the oviduct of the black-faced ewe (Sheep C), after ligating the oviduct of Sheep C so that the embryo could not enter the uterus. Sheep C serves as a living culture for the embryo and is called an intermediate recipient.
Be careful that the reconstructed eggs are transferred into the oviduct of the C-goat for 6 days, and then the embryos are flushed from the oviduct, and those embryos that have developed normally to the mulberry and blastocyst stages are selected.
Select 1-3 mulberry or blastocyst embryos and transfer them to the uterus of Scottish Blackface sheep (Dinkum). After the embryos are transferred to the uterus, they continue to develop and finally give birth to "Dolly". This ewe is called the "surrogate mother".
About 434 eggs were used, 277 reconstructed eggs were obtained, and 6 days after transfer to the intermediate recipient, 247 embryos were flushed out, of which 29 (11.7%) developed into mulberry embryos and blastocysts. The 29 embryos were transferred to 13 surrogate mothers, resulting in 1 "Dolly", with a lambing rate of only 3.4%. Based on the number of reconstructed eggs, the lambing rate was less than 4 ‰. This technology needs to be improved. In addition, it should be noted that the cloning of sheep technology does not do a complete copy of the cytoplasm of the nucleated egg cells will also contain a small amount of genetic material, which can also play an important or even decisive role in the development of the embryo. Biological inheritance is the result of the interaction between the nucleus and the cytoplasm***. Cytoplasmic genes are also DNA fragments , and their carriers are mainly some cellular organelles, such as plastids, mitochondria and so on. Cytoplasmic genes are to some extent independent and are generally not interfered with by nuclear genes. In contrast to nuclear genes, although the nucleus contains 99.9% of the genetic information, the expression of individual traits can still be influenced by the egg cytoplasm. Therefore, theoretically, Dolly the sheep is not an exact replica. Since "Dolly" is only a lone sheep, some people believe that it is inaccurate to say that "Dolly" is a cloned animal. Although only one "Dolly" has been obtained, it is a major scientific achievement that has caught the attention of the world.
Fifth, the significance of cloning technology and economic value
The magnificent history of mankind is to a large extent driven by the development of technology: metal manufacturing and improved agriculture to make civilization out of the Stone Age; 19th-century industrial revolution led to the emergence of big machines and big cities; to the 20th century, physics wore the crown. Physicists split the atom, revealed the wondrous worlds of relativity and quantum theory, and exploited tiny wafers of silicon. They changed the world with atomic bombs, transistors, lasers and miniature integrated circuits. Now, many experts believe that humankind is ready to meet the future with a new wave of technological development. As Robert Cole, the 1996 Nobel Prize winner and a chemist at Rice University, said, "This is the century of physics and chemistry, but the next century will clearly be the century of biology." Many scientists believe that the century of biology has come early, marked by the birth of Dolly the cloned sheep.
The breakthrough in cloning technology has shocked the world. People are worried about the self-replication of human beings and tend to ignore the application and significance of other aspects. In fact, it has significant theoretical value and broad application prospects in basic life sciences, medicine, home industry scientific research and production, and there is a huge potential economic benefits. In the next 5 ~ 20 years, will gradually form and cause a world-wide new biotechnology industrial revolution.
⒈ in the basic life sciences, from the previous gene function research is mainly carried out in a few animals such as mice, and now in a variety of animals can be realized, which is conducive to a clearer revelation of the function of genes and the nature of life; to provide one of the most effective means of studying the development of mammalian cellular totipotency and nucleoplasmic relationships; can also be cloned a variety of endangered animals such as pandas, national treasures, golden monkeys and even albino dolphins.
Peak in medical science, can provide nuclear genotypes for medical science research completely consistent experimental animals, which is conducive to medical scientists to study the current has not yet found an effective treatment for the disease, and to reveal the pathogenesis; for its de-differentiation mechanism of the study, to help anti-aging and its mechanism of the study.
3 In agricultural science, we can rapidly breed and expand the breeding of excellent animals with strong disease resistance and high production performance; we can study the pathogenesis of animals and seek new effective therapeutic drugs.
How to meet the challenges of the "cloning era"
The success of cloning technology marks the breakthrough of the last technical obstacle of "copying" mammals. With this, it has become theoretically possible to replicate human beings. Therefore, cloning technology not only brings us benefits, but also poses a serious challenge to human beings. This technology, once applied to human beings, will have extremely serious consequences for human society.
1 ⒈ human beings from sexual reproduction back to asexual reproduction,