In July 1996, in a sheepfold on the outskirts of Edinburgh, Scotland, a cute little sheep landed on the ground with a series of "baaaah" sounds. Although the owner immediately named it "Dolly", the owner kept silent about its arrival for about 7 months, so the world knew nothing about it. It was not until the necessary registration procedures were completed for "Dolly" - on February 23, 1997, after the patent application was filed, that the owner announced that "Dolly" was the first in the world to use fully differentiated mammary gland cells from a 6-year-old adult ewe. Successful asexual reproduction of lambs. Its owner is a research team headed by Ian Wilmut and Keith Campbell from the Roslin Institute in the UK. The news spread like wildfire and immediately attracted widespread attention around the world, becoming one of the most sensational scientific research results in recent years.
As we all know, under normal circumstances, mammals reproduce through viviparous fertilization. Among them, the combination of eggs and sperm to form fertilized eggs is the first important step in mammalian reproduction. However, the cloned sheep "Dolly" was born without the key link of sperm and egg union.
To be more precise, the cloned sheep "Dolly" has no father but three mothers. The process of its birth is as follows: scientists from the Roslin Institute first removed an ordinary cell with no reproductive function from the mammary gland of an adult Dorset ewe sheep born in Finland, and isolated the nucleus of the cell for later use. . Then, they took out an unfertilized egg cell from the ovary of a Scottish black-faced ewe, took out the nucleus of the egg cell, and replaced it with the nucleus isolated from the mammary gland cell of the first ewe. The "tuned" egg cells are activated under the action of electric sparks, causing them to begin cell division like a normal fertilized egg. After the egg cell divides to form an embryo, it is then transplanted into the uterus of another Scottish Blackface ewe to allow normal embryonic development. This third sheep gave birth to Dolly after a normal pregnancy.
In the authoritative British science weekly "Nature" published on February 27, 1997, the British Roslin Institute research team headed by Ian Wilmut and Keith Campbell published their Research results. Wilmut said: "Dolly" inherited the genetic characteristics of his biological mother (the first ewe to provide the nuclei of mammary cells). It can also be said that "Dolly" is almost a 100% "replica" of the first ewe.
The birth of the cloned sheep "Dolly" ushered in a new era of asexual reproduction of mammals.
Since the 1970s, scientists from many countries have obtained cloned frogs, cloned pigs, cloned goats and even cloned monkeys through hard work. However, these cloned animals are all carried out through nuclear transfer of embryonic cells, and they are not always cloned. It’s not really asexual reproduction. Because the embryonic cells themselves are produced through sexual reproduction, half of the genome in the nucleus comes from the father and half from the mother. The cloned sheep "Dolly" is a nuclear transplant using highly differentiated somatic cells. All its genome comes from its mother. This is true asexual reproduction.
Scientists pointed out that the most important scientific significance of "Dolly" being born smoothly and growing up healthily is that it is the first time that nuclear transplantation has been carried out using highly differentiated somatic cells of animals. This is unprecedented and undoubtedly Another major breakthrough in the field of science and technology in the 20th century. Its most important theoretical significance is to prove that a fully differentiated somatic cell can completely return to its early primitive cell state and can retain all genetic information intact like an embryonic cell. This is completely consistent with previous scientific conclusions. Not the same. The news of the birth and healthy growth of "Dolly" the sheep was like a powerful nuclear warhead, shattering the "golden rule" that the international biology community had long believed in, ushering in a new era of biology.