Since the foreign news media 1997 (the official scientific paper was published in1Nature published on February 27, 1997) reported on February 23 that Scottish scientists successfully bred somatic cloned sheep, it caused a shock wave all over the world, which was called "cloning storm" by Professor Wu Hao, a famous geneticist in China. For a scientific achievement, the response is so extensive and strong, from the press, scientific circles, to philosophy and ethics, to government departments and legislatures, and then to the general public, all pay attention to cloning technology. What is cloning, the value and significance of this technology, and how to face the "cloning era" have become the focus of discussion.
I. The concept of cloning
As we all know, the reproduction of living things is accomplished through reproduction. There are two ways of biological reproduction: one is called sexual reproduction and the other is called asexual reproduction.
Sexual reproduction is a reproductive mode in which bisexual germ cells (sperm and eggs) fuse and develop into offspring. Asexual reproduction does not combine hermaphroditic germ cells, but forms individuals through the division and reproduction of the organism itself or the growth and development of its somatic cells. Asexual reproduction is common in plants and some animals (such as single-celled animals and lower animals).
Cloning is a transliteration of the English word "clone", which comes from the Greek word klon, meaning seedling or twig, and refers to some plants that reproduce asexually or nutritionally. With the passage of time and the development of science, its meaning has increased a lot, such as a group of cells produced by a cell in vitro culture; DNA sequences produced by "parent" sequences, and so on. In a word, cloning refers to obtaining a group of cells or individuals with identical genes from a cell or individual through asexual reproduction.
The Monkey King in China's famous classic The Journey to the West can "transform" many the Monkey King as long as he pulls out a hair from his mouth and blows a fairy tale. Because pulling a finger on a finger will inevitably bring a group of cells, and this group of cells can cultivate a group of the same Sun Shengda. This is also asexual reproduction. It's just that Sun's skills are so high that he can "clone" thousands of himself in an instant. In short, cloning is asexual reproduction, that is, "replication" and "replication".
Second, plant cloning.
Asexual reproduction (cloning) is originally a low-level reproductive mode. The lower the level of biological evolution, 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. Because lower organisms, such as microorganisms, reproduce through self-division, and the genetic material of the offspring after division is exactly the same as their parents, in this sense, microorganisms have no "individuals" and they have not died. Although there are some differences between the parents and offspring of microorganisms in a strict sense, because their external nutritional environment will still be different, from the perspective of higher animals, this difference seems too insignificant. When this difference can be ignored, people can say that they are immortal to microorganisms. Death is the product of biological evolution to a higher stage. Normal cells or cancer cells cultured in vitro by cloning technology in biomedical research are also called "immortalized cell lines", that is, these cells are "immortal".
Biomedical research has entered the microscopic level. It is a very arduous task to cultivate immortal cell lines of normal or abnormal cells by cloning technology, but it has been paid more and more attention by scientific and medical circles in various countries. In agriculture, people have cultivated plants suitable for human needs by cutting and layering. In animal husbandry, countries are conducting research on cloning technology to produce more excellent animals. However, in higher organisms, the development from an adult somatic cell to an adult is a great development of cloning technology.
Many years ago, researchers at Cornell University in the United States stirred mature carrots at high speed to obtain single carrot cells, and then put these single cells into a growth medium to cultivate carrots with the same genes. This experiment confirmed the theory of plant cell totipotency. The so-called totipotency theory of plant cells means that every cell of plants, including somatic cells, has the potential to develop into a complete individual.
The theory of plant cell totipotency has been widely proved in the plant world. Now we can obtain a complete plant from any living cells, tissues and organs of plants by artificial culture in vitro, and produce many plants. This technique is called tissue culture. It has been used for industrialized production of test-tube seedlings of flowers and crops (such as sugarcane).
Third, the process of animal cloning.
The research of animal asexual reproduction has always been a subject explored by scientists. Because human beings have been cultivating livestock breeds through sexual reproduction for thousands of years, the result is that some excellent individuals or groups have been produced. They can meet people's needs and desires better than ordinary individuals. For example, a cow with a particularly high milk yield, a flock of sheep with a particularly high wool yield, an award-winning racehorse or an excellent police dog. However, the offspring who have sexual reproduction do not necessarily behave like their parents, and some even behave worse than their parents. The reason is that eggs or sperm only carry any half of the alleles that make up the parents, and the alleles can have almost unlimited combinations, so different offspring will be produced. There are great differences between brothers and sisters, because it is extremely difficult to have exactly the same genotype.
So it is difficult to maintain a phenotype through sexual reproduction. If an ideal phenotype is obtained, such as a cow with high milk yield, it is obviously valuable from an economic point of view to maintain, expand and reproduce this phenotype through asexual reproduction, that is, to produce many genetically identical individuals.
Egg cells are cultured into adults.
195 1 ~ 1959, Zhu Xian, a famous cell biologist in China, stimulated toad's egg cells with a glass needle with a diameter of 10 ~ 13um, and for the first time in the world, 25 adult toads, namely fatherless toads, were cultivated. They can live up to eight months.
Germ cells were used in the above experiments. Can animal bodies be obtained by culturing somatic cells? That is to say, plant cells are totipotent, and so are animal cells? There is no doubt that every animal cell, including somatic cells, has a complete set of genes of this species, but it has not been successful to culture somatic cells directly into animal adults. In order to prove that animal cells are totipotent, biologists have carried out a large number of nuclear transplantation experiments.
2. Nuclear transfer test
1939, scientists conducted the first nuclear transplantation experiment in amoeba. They transplanted the nucleus into the same kind of enucleated amoeba, and as a result, the recombinant amoeba could grow and reproduce.
Since 1963, Tong Dizhou, a famous biologist in China, has carried out a large number of nuclear transfer experiments in fish. 1980, they used carp blastocyst nucleus as donor nucleus and unfertilized mature eggs of crucian carp as recipient, and 2.7% of transplanted eggs developed into adult fish. The main characteristics of carp and crucian carp nuclear transfer fish are the same as those of carp, but the number of vertebrae is the same as that of crucian carp, and the number of lateral scales is between these two kinds of fish. The growth rate of this cell-engineered fish is 22% faster than that of carp, and it has been widely popularized in production.
1966, scientists conducted a nuclear transplantation experiment with the amphibian Xenopus laevis. They transferred the nuclei of tadpoles' intestinal cells into enucleated eggs, and as a result, 1.5% of the recombinant cells developed into adults. Their experiments proved for the first time that animal somatic cells are totipotent, but they have not been proved in mammalian somatic cells.
13. Cloning mammals with embryonic cells.
1986, British scientists used sheep 8-cell embryonic cells (cells before 8-cell embryos can show totipotency) as donor cells, and sheep egg cells as donor cells. As a result, the recombinant cells can develop into sheep adults, and then animals such as cattle, mice, rabbits and monkeys can be cloned from embryonic cells. It should be pointed out that this experiment is not to copy rams or ewes, but to copy their offspring, so there are still some shortcomings or defects in the experiment.
In China, mammals were cloned from embryonic cells, and in the late 1980s, they were cloned again. Sheep were cloned by Northwest Agricultural University and Jiangsu Agricultural College at 199 1. 1993, Institute of Development of China Academy of Sciences and Agricultural College of Yangzhou University cloned goats. 1995 south China normal university and Guangxi agricultural university cloned cattle. In addition, Hunan Medical College also cloned mice. However, cloning mammals from somatic cells other than embryonic cells was initiated by British scientist Wilmut.
Fourth, the birth of "Dolly"
"Dolly" is the first lamb in the world that was obtained by using somatic cells-mammary epithelial cells through nuclear transfer technology and complicated manual operation. The operation process is as follows:
1. Take out the egg from Scottish black-faced ewe (a kind of sheep) and suck the genetic material of the egg to make it into an egg with only cytoplasm.
Mammary epithelial cells were taken from ewes (B sheep) in the third trimester of pregnancy and cultured for 3-6 generations in vitro. These cells are treated with drugs to control their development and keep them at rest. This is a crucial step. Then resting cells are used as donor cells.
13. Introduce donor cells into the zona pellucida cavity of the egg. Then, donor cells and eggs are fused by electrical pulse stimulation to form reconstructed eggs.
The reconstructed egg was transplanted into the oviduct of a black-faced ewe (sheep C), and the oviduct of sheep C was ligated before, so that the embryo could not enter the uterus. C sheep play the role of cultivating embryos in vivo, which is called intermediate receptor.
Six days after the reconstructed eggs were transferred into the fallopian tube of C sheep, the embryos were washed out of the fallopian tube, and the embryos that developed normally to the morula stage and blastocyst stage were selected.
6. Transplant 1-3 morula or blastocyst into the uterus of Scottish black-faced sheep (Ding sheep). After the embryo was transplanted into the uterus, it continued to develop and finally gave birth to Dolly. This ewe is called "surrogate mother"
About 434 eggs were used in this project, and 277 reconstructed eggs were obtained. Six days after transplantation into the intermediate recipient, 247 embryos were rushed out, of which 29 (1 1.7%) developed into morula and blastocyst. Twenty-nine embryos were transferred to 13 surrogate mothers, and finally 1 Dolly was born, with a lambing rate of only 3.4%. If calculated by the number of reconstructed eggs, the lambing rate is less than 4 ‰. It can be seen that this technology needs to be improved. In addition, it should be noted that sheep cloning technology has not been completely replicated, and the cytoplasm of enucleated eggs will also contain a small amount of genetic material, which can also play an important or even decisive role in embryo development. The inheritance of organisms is the result of the interaction between nucleus and cytoplasm. Cytoplasmic genes are also DNA fragments, and their carriers are mainly some organelles, such as plastids and mitochondria. Cytoplasmic genes are independent to a certain extent and are generally not interfered by nuclear genes. Compared with nuclear genes, although the nucleus contains 99.9% genetic information, the expression of individual traits will still be affected by the cytoplasm of eggs. So theoretically, "Dolly" sheep is not a complete replica. Because "Dolly" is only a lonely one, some people think that the statement that "Dolly" is a cloned animal is not accurate. Although only 1 "Dolly" has been obtained so far, it is a great scientific achievement that attracts worldwide attention.
Significance and economic value of verb (verb abbreviation) cloning technology
The magnificent human history is largely driven by technology: metal manufacturing and improved agriculture have separated civilization from the Stone Age; /kloc-the industrial revolution in the 0/9th century led to the rise of big machines and big cities; In the 20th century, physics was crowned. Physicists split atoms, revealed the wonderful world of relativity and quantum theory, and developed and utilized small silicon wafers. They changed the world through atomic bombs, transistors, lasers and microchips. Now, many experts believe that human beings are ready to meet a new wave of scientific and technological development in the future. As Robert Curl, a chemist at Rice University and winner of the 1996 Nobel Prize, said, "Now is the century of physics and chemistry, but the next century will obviously be the century of biology." Many scientists believe that with the birth of Dolly, a cloned sheep, the century of biology has arrived ahead of schedule.
The breakthrough of cloning technology shocked the world. People worry about human self-replication, but they often ignore the application and significance of other aspects. In fact, it has great theoretical value and broad application prospects in the research and production of basic life science, medicine and family science, and has great potential economic benefits. In the next 5 ~ 20 years, it will gradually form and cause a new world biotechnology industry revolution.
1. In the basic life science, the study of gene function has been carried out in a few animals, such as mice, and now it can be realized in many animals, which is helpful to reveal the gene function and life essence more clearly; It provides one of the most effective means to study the totipotency of mammalian cell development and the relationship between nucleus and cytoplasm. You can also clone various endangered animals, such as giant pandas, golden monkeys and even baiji.
In medicine, it can provide experimental animals with exactly the same nuclear genotype for medical research, which is beneficial for medical scientists to study diseases that have not yet found effective treatments and reveal the pathogenesis; The study of dedifferentiation mechanism is helpful to the study of anti-aging and its mechanism.
3. In agricultural science, excellent animals with strong disease resistance and high production performance can be quickly cultivated and propagated; We can study the pathogenesis of animals and seek new and effective therapeutic drugs.
How can intransitive verbs meet the challenge of "cloning age"
The success of cloning technology indicates that the last technical obstacle of "copying" mammals has been broken. In this way, it is theoretically possible to copy humans. Therefore, cloning technology not only brings us benefits, but also brings severe challenges to mankind. Once this technology is applied to human beings, it will bring extremely serious consequences to human society.
The return of human beings from sexual reproduction to asexual reproduction is undoubtedly a huge retrogression.
6. Without parents and affection, the "clone" society would become heartless.
3. "Clone" may reproduce through sexual reproduction in adulthood, and a large number of close relatives may get married unconsciously, with disastrous consequences.
From the sociological point of view, the continuous development and progress of mankind depends on everyone's continuous efforts and struggles. In addition to personal ideals, this power comes from people's obligations to society and family. If there is no obligation to support the elderly and raise the next generation, this power will be greatly reduced, which is also unfavorable to the development of the whole society.
A "replica" of a scientist may not become a scientist. Besides congenital reasons, acquired factors also play an important role in people's success. If these "replicas" are the burden of scientists, wouldn't society go backwards if they didn't study hard? Furthermore, what will society do if someone clones a large number of mentally retarded people in order to retaliate against society? If someone frantically "copies" a madman like Hitler and "cultivates" the day after tomorrow, it will make people feel even more horrible. ...
From the birth of cloned sheep, we are reminded of the energy relationship proposed by Einstein, a great scientist in 1905, which shows that there is huge energy in the nucleus. It never occurred to him that this theory became an important theory for making atomic bombs. If cloning technology is applied to human beings, it will be a great retrogression in the biological world. So we think that scientists are innocent in scientific research, and the problem is how to apply them.
We should "foster strengths and avoid weaknesses" and actively use the beneficial side of cloning technology to benefit mankind. At the same time, governments should strengthen legislation, strengthen supervision and prohibit the application of cloning technology to human beings in order to avoid the occurrence of human tragedies.
In short, the emergence and maturity of a new technology will inevitably bring new challenges and problems. With the improvement of moral law, people will eventually make good use of it.