As we all know, under normal circumstances, mammals reproduce by viviparous fertilized eggs. Among them, the combination of eggs and sperm into fertilized eggs is the first important link in mammalian reproduction. However, the birth of Dolly, a cloned sheep, lacked the key link of sperm-egg combination.
More precisely, Dolly the cloned sheep has no father, only three mothers. The process of its birth is as follows: scientists at Roslin Institute first took out an ordinary cell from the mammary gland of an adult Dorset ewe born in Finland and separated its nucleus 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 sheep's egg cell, and replaced it with the nucleus separated from the mammary gland cell of the first ewe, and then activated the "on-off" egg cell under the action of electric spark, making it start to divide like a normal fertilized egg. After the egg cell divides to form an embryo, it is transplanted into the uterus of another Scottish black-faced ewe to make it develop normally. The third sheep gave birth to Dolly after normal pregnancy.
Nature, the authoritative British scientific weekly, was published on February 27th 1997, by Ian? Wilmot and Keith? The research team led by Campbell published their research results. Wilmut pointed out: "Dolly" inherited the genetic characteristics of her biological mother (the first ewe to provide breast nuclei). It can also be said that Dolly is almost a 100% copy of the first ewe.
The birth of Dolly the cloned sheep opened a new era of asexual reproduction of mammals.
Since the 1970s, scientists in many countries have obtained cloned frogs, cloned pigs, cloned goats and even cloned monkeys through their efforts, but these cloned animals are all nuclear transplanted through embryonic cells, not really asexual reproduction. Because the embryonic cell itself is produced by sexual reproduction, half of the genome in its nucleus comes from the father and half from the mother. Dolly, a cloned sheep, is a nuclear transfer of highly differentiated somatic cells, and its genome comes from its female parent, which is really asexual reproduction.
Scientists pointed out that the most important scientific significance of Dolly's successful birth and healthy growth lies in the unprecedented use of highly differentiated animal somatic cells for nuclear transplantation for the first time, which is 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 state, and it can also completely preserve all genetic information like an embryonic cell, which is completely different from previous scientific conclusions. The news that Dolly the sheep was born and grew up healthily, like a powerful nuclear warhead, shattered the "golden rule" that the international biological community had long believed in and opened up a new era of biology.