Clone" is transliterated from the English "clone" and has three different levels of meaning in the field of biology.
1. At the molecular level, cloning generally refers to DNA cloning ( Also called molecular cloning), it means inserting a specific DNA fragment into a vector (such as plasmid and virus, etc.) through recombinant DNA technology, and then replicating itself in the host cell to obtain a large number of identical DNA fragments. "Population".
2. At the cellular level, a clone is essentially a population of cells formed by the division of a single ancestral cell, e.g. A group of cells with the same genetic background formed by dividing cells in culture medium in vitro for several generations is a cell clone. For another example, in vertebrates, when foreign substances (such as bacteria or viruses) invade, it will occur. Specific recognition antibodies are produced through immune reactions. All plasma cells that produce a specific antibody are divided from one B cell. Such a plasma cell population is also a cell clone. Cell cloning is a low-level form of reproduction - asexuality. Reproduction, that is, without sexual union, the offspring and the parent have the same genetics. The lower the level of biological evolution, the more likely it is to adopt this method of reproduction.
3. At the individual level, cloning means. A group of two or more individuals with identical genotypes. For example, two identical twins are a clone! Because they come from the same egg cell, their genetic background is exactly the same. "Dolly" cannot be said to be a clone! Because "Dolly" is just a single clone. Only if those British embryologists can transplant two or more identical nuclei into two or more identical enucleated egg cells, a clone will be obtained. The word clone can only be used to describe two or more "Dolly"s with the same genetic background. Therefore, in the sensational paper published in Nature in February 1997, the author did not refer to "Dolly". Said to be a clone.
In addition, cloning can also be used as a verb, which means the process of obtaining the above-mentioned DNA, cells or individual groups.
2. Cloning technology<. /p>
1. DNA cloning
There are many methods for DNA cloning. The basic process is shown in the figure below (not to scale)
As you can see, we get DNA can be used in many aspects of biological research, including the analysis and processing of specific DNA base sequences, and the mass production of valuable proteins in the biotechnology industry.
2. Cloning
(1) Cloning of plant individuals
In the 1950s, botanists used carrots as model materials to study whether genetic material was lost in differentiated plant cells. They were surprised to find that a complete plant could develop from a single highly differentiated carrot cell! From this, they believed that plant cells are totipotent. The genetic background of the carrot population developed from more than two somatic cells in one carrot is exactly the same, so it is a clone. Such a plant cloning process is a complete asexual reproduction process!
(2) Cloning of individual animals
① The birth of “Dolly”
1997 On February 27, Ian Wilmot's scientific research team at the Roslin Institute in Edinburgh, UK, announced to the world that the world's first cloned sheep, "Dolly", was born. This news immediately caused a sensation around the world. .
The creation of "Dolly" is related to three ewes. One is a Finnish Dorset ewe sheep that is three months pregnant, and the other two are Scottish black-faced ewe sheep. The Finnish Dorset ewe provided the complete set of genetic information, that is, the nucleus (called the donor); a Scottish Blackface ewe provided the egg cell without a nucleus; and another Scottish Blackface ewe provided the development of the sheep embryo. The environment - the uterus, is the "birth" mother of "Dolly" sheep. The entire cloning process is briefly described as follows:
Mammary gland cells were taken out from the mammary glands of Dorset ewe sheep in Finland and put into low-concentration nutrient culture medium. The cells gradually stopped dividing. This cell is called It is a donor cell; a Scottish black-faced ewe is injected with gonadotropin to induce ovulation, the unfertilized egg cell is taken out, and its nucleus is immediately removed, leaving a nucleus-free egg cell. This cell is called the recipient. cells; the method of electric pulse is used to fuse the donor cell and the recipient cell, and finally a fused cell is formed. Since the electric pulse can also produce a series of reactions similar to the natural fertilization process, the fused cell can also behave like a fertilized egg. The cells divide and differentiate in the same way to form embryonic cells; the embryonic cells are transferred to the uterus of another Scottish black-faced ewe, and the embryonic cells further differentiate and develop, finally forming a lamb. Dolly lambs are born with the exact same appearance as Dorset ewes.
A year later, another group of scientists reported that more than 20 cells were obtained by transplanting the nuclei of mouse cumulus cells (highly differentiated cells surrounding the periphery of oocytes) into oocytes with their nuclei removed. Only fully developed mice.
If there is only one "Dolly" and it is not enough to be called a cloned sheep, these mice are truly cloned mice.
② The basic process of cloning mice through nuclear transfer
In this experiment, cumulus cells were obtained through the following process: through several consecutive injections of chorionic gonadotropin, Inducing female mice into a state of high egg production. Complexes of cumulus cells and oocytes were then collected from the oviducts of female mice. Cumulus cells were dispersed by hyaluronic acid treatment. Select cumulus cells with a diameter of 10-12 microns as the nucleus donor (previous experiments have shown that if the nuclei of cumulus cells with smaller or larger diameters are used, the oocytes that have undergone nuclear transplantation will rarely develop to the 8-cell stage. ). The selected cumulus cells were kept in a certain solution environment and the nuclei were transplanted within 3 hours (different from this, the breast cells used as nucleus donors when obtaining "Dolly" were first passaged in the culture medium for 3 hours. -6 times)
Oocytes (generally in meiotic metaphase II) were collected from female mice of different species by a method similar to that described above. Carefully remove the nucleus of the oocyte using a thin tube with a diameter of approximately 7 microns under a microscope, and try not to remove the cytoplasm. Also carefully remove the nucleus of the cumulus cells and remove as much cytoplasm as possible (by moving the removed nucleus back and forth several times in the glass tube to remove a small amount of cytoplasm). Inject directly into the oocyte from which the nucleus has been removed within 5 minutes after the nucleus is removed. The oocytes that have undergone nuclear transfer are first placed in a special solution for 1-6 hours, and then divalent strontium ions (Sr2+) and cytostatin B are added. The former activates the oocyte, and the latter inhibits the formation of polar bodies and the elimination of chromosomes. The treated oocytes are then taken out and placed in a special solution without strontium and cytostatin B to cause cell division to form embryos.
Embryos of different stages (from the 2-cell stage to the blastocyst stage) were implanted into the fallopian tubes or uterus of pseudopregnant female mice that had been mated with ligated male mice a few days ago. Fully developed fetal mice are surgically removed after approximately 19 days.
At present, animals cloned by embryonic cell nuclear transfer include mice, rabbits, goats, sheep, pigs, cows and monkeys. In China, in addition to monkeys, other animals are cloned, and goats can also be cloned by continuous nuclear transfer. This technology goes further than embryo segmentation technology and will clone more animals. Because the more times the embryo is divided, the fewer cells each share, and the worse the ability of the individual to develop. There is only one animal cloned by somatic cell nuclear transfer, and that is Dolly the sheep.
3. The gospel of cloning technology
1. Cloning technology and genetic breeding
In agriculture, people have used "cloning" technology to cultivate a large number of high-quality, high-yielding varieties that are resistant to drought, lodging, and pests and diseases, which has greatly increased grain yields. In this regard, our country has entered the forefront of the world's most advanced countries.
2． Cloning technology and the protection of endangered organisms
Cloning technology is a boon to the protection of species, especially rare and endangered species, and has great application prospects. From a biological perspective, this is also one of the most valuable aspects of cloning technology.
3． Cloning Technology and Medicine
In the modern era, doctors can perform transplant operations on almost all human organs and tissues. But in terms of science and technology, rejection in organ transplantation is still the most troublesome thing. The reason for rejection is poor tissue compatibility due to tissue mismatch. If the organs of a "cloned human" are provided to an "original human" for organ transplantation, there will be absolutely no worries about rejection, because the genes and tissues of the two are matched. The question is, is it humane to use "human clones" as organ donors? Is it legal? Does it make financial sense?
Cloning technology can also be used to reproduce valuable genes in large quantities. For example, in medicine, people use "cloning" technology to produce insulin to treat diabetes and growth hormone to make patients with dwarfism grow taller again. and streptoxin, which can resist various viral infections, etc.
The well-known first cloned higher animal - Dolly
Dolly the cloned sheep
Dolly the sheep was born on July 5, 1996, and was first presented to the public in 1997. Public Disclosure. It was named the first of the world's top ten scientific and technological advances in 1997 by the American "Science" magazine, and was also one of the most eye-catching international news of the year. Scientists believe that the birth of Dolly marks the advent of a new era of biotechnology.
In the process of breeding Dolly the sheep, scientists used somatic cell cloning technology. In other words, a somatic cell is extracted from an adult sheep, and then the nucleus of this somatic cell is injected into the egg cell of another sheep, and the egg cell has had its nucleus removed. Finally, the newly synthesized egg cell is in the third sheep. The in-utero development of Dolly the Sheep. In theory, Dolly inherited the genetic characteristics of the sheep that provided the body cells. The technology used to breed Dolly the sheep has become the standard process for creating somatic cell cloned animals today.
Cloning animals, including human cloning, has become the most controversial scientific topic today. Technically, it took scientists from Scotland's Roslin Institute more than two hundred experiments to successfully breed Dolly, and it was discovered in 2001 that it had arthritis-like symptoms.
Scientists believe this reflects in some ways flaws in current cloning technology. Dolly's untimely death is expected to further trigger relevant debates.
Dolly the sheep died of lung disease
According to the Roslin Institute, Dolly had been coughing non-stop for a week before being diagnosed. On February 14, a veterinarian diagnosed Dolly with severe progressive lung disease.
The so-called "progressive" disease means that the patient's condition continues to develop and worsen, and his life is in danger. In view of this situation, the institute decided to implement "euthanasia" for Dolly. They really couldn't bear to watch Dolly die in depression. They hoped that this cute little boy who had enjoyed the joy of life and brought countless surprises to the world The sheep passed away peacefully.
Premature death sparks debate
Dolly's death has once again sparked a debate about whether cloned animals will "aging prematurely". Dolly was created through somatic cell cloning by Professor Ian Wilmot and others at the Roslin Institute. Professor Ian Wilmot said that he had discovered that Dolly the sheep had arthritis in his left hind leg about a year ago, and that this typical "disease of old age" was likely to be a problem for Dolly, who was still young at the time. This means that the current cloning technology is not perfect yet.
Following the advent of Dolly, cloning technology has developed to a certain extent in recent years. Scientists from various countries have successively cloned cows, rats, pigs and other animals. However, at the same time, scientists have also discovered that some cloned animals exhibit " "Premature aging" signs, which are considered to be the harm to the health of cloned animals caused by the imperfect cloning technology itself. However, the scientific community has not yet reached a final conclusion on this.
Willmott said they will conduct a careful examination of Dolly's body to further determine the cause of his death. He also said: "It is important that not just us, but all the scientists who clone animals, continue to observe the health of cloned animals throughout their lives."
Dolly's Immortal Contribution
Dolly was the first human being to successfully clone using adult animal somatic cells. The birth of Dolly opened a new page in the field of molecular biology. It forced scientists to re-examine the existing theories of embryonic development and foreboding that humans might one day clone themselves. At the same time, somatic cell cloning technology also provides feasible ideas for curing difficult diseases such as Parkinson's disease from the perspective of cultivating cells in the future.
Dolly kept bringing us surprises one after another during his lifetime. It first "tied the knot" with a Welsh goat named David, and later gave birth to their first "love child" Bonnie in April 1998, thus proving that cloned animals can also have children. In 1999, Dolly's family welcomed three more adorable baby sheep.
The Dolly problem needs to be solved urgently
Dolly the sheep, the world’s first somatic cell cloned animal, left us forever after bringing us excitement, confusion and controversy. Just like when it came out, Dolly the sheep, whose lifespan was only 6 and a half years old, died young in the prime of life, once again attracting the attention of the world. As a symbol of cloning technology and its applications, Dolly the sheep has brought controversy and left mysteries behind. The biggest mystery is whether cloned animals will age prematurely. Some people call it the Dolly the Sheep problem.
The so-called Dolly the Sheep problem refers to whether the age of a cloned animal should be calculated from 0 years old, cumulatively from the age of the cloned animal, or from an age in between. As far as Dolly the sheep is concerned, since it was cloned from the somatic cells of a 6-year-old ewe, is it 6 and a half years old, 12 and a half years old, 8 or 10 years old?
This problem has puzzled people since Dolly the Sheep came out. In the first few years, Dolly the sheep grew, developed and gave birth normally, which gave great hope to the first theory. However, in January 2002, scientists discovered that Dolly the sheep suffered from arthritis in his left hind leg, a typical " "Symptoms of old age", this phenomenon of premature aging increases the possibility of the second and third speculations. Now, Dolly the sheep died in his prime from a lung infection common among elderly sheep, which undoubtedly adds weight to the second speculation.
Is the premature aging of cloned animals an accidental phenomenon, an inevitable result of cloning technology, or is it caused by the imperfection of current cloning technology? This requires further research by scientists.
Currently, there are many health problems in cloned animals. Miscarriage, premature death, and deformities in cloned animals all over the world are very serious. Dolly the sheep is considered healthy and long-lived among the large number of cloned animals currently available. It has experienced the entire process of birth, development, childbirth and death. Scientists have a lot of debates about animal cloning, but one thing is generally agreed upon: cloning technology is far from mature, and you need to be extra cautious when applying cloning technology, and the problem of Dolly the Sheep needs to be solved as soon as possible.
Clone is the transliteration of English clone. Simply put, it is an artificially induced asexual reproduction method. But cloning is different from asexual reproduction. Asexual reproduction refers to a reproductive method that produces offspring from only one organism without the combination of male and female reproductive cells. Common ones include sporulation, budding, and fission. The production of new individuals from the roots, stems, leaves, etc. of plants through layering or grafting is also called asexual reproduction. Animals such as sheep, monkeys and cattle cannot reproduce asexually without artificial manipulation. Scientists call the process of artificial genetic manipulation of animal reproduction cloning, and this biotechnology is called cloning technology.
Convert the word clone from a noun to a verb, and call nuclear transplantation nuclear cloning, and clones of DNA molecules obtained through genetic engineering are called molecular cloning. Cloning here is an operation to achieve asexual reproduction, which is a microscopic operation or molecular biology operation, rather than asexual reproduction (or asexual reproduction operation) in the general sense. This is perhaps why the term cloning survives and is not replaced by asexual reproduction.
The basic process of cloning is to first transplant the nucleus of a donor cell containing genetic material into an egg cell with the nucleus removed, then use microcurrent stimulation to fuse the two into one, and then promote the new cell. The embryos are developed through division and reproduction. When the embryos develop to a certain level, they are then implanted into the uterus of an animal to make the animal pregnant. An animal with the same genes as the person who provided the cells can be born. If the donor cells are genetically modified during this process, the same changes will occur in the genes of the offspring of asexually reproduced animals.