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).
It can be said that Wu Cheng'en, a great writer in China in the Ming Dynasty, once described the idea of cloning wonderfully-the Monkey King often pulled out a handful of monkey hair at a critical moment and turned it into a large group of monkeys, and the monkey hair turned into a monkey is a cloned monkey.
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, and the egg cell 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 nucleus of mouse embryonic cells into enucleated fertilized eggs of black mice, they were artificially cultured in test tubes for four days, and then implanted into the uterus of white mice. After hundreds of gray, black and white operations, the white mouse finally gave birth to three little gray mice.
The British magazine Nature published on February 27th last year 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 did Dolly sheep "create"? 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."