In February 1997, an article published in the journal Nature caused a sensation in the field of science. The birth of Dolly the cloned lamb became the focus of people's talk for a while, as if this great discovery was about to lead people to new technological developments. Cloning technology does not require the union of sperm and eggs, only a few cells and the outer shell of the egg to cultivate a living life. This new technology that sounds lofty and makes people feel at science is not actually made in a day, but has been bred for hundreds of years, through the efforts of hundreds of biologists, embryologists, zoologists and other experts in various fields.
Strange brain hole
A hundred years ago, no one knew how a fertilized embryonic cell divided into 2 cells, 4 cells, 8 cells... It then differentiates into different cell types to make up organs. So many interesting ideas have been proposed, such as some people think that the egg itself carries a small person, some people speculate that sperm carries a small person, and some people think that the earliest embryos of each species give birth to all future embryos, just like Russian matryoshka dolls.
The Little Man in Sperm Source: Smithsonian Magzine
An experiment poking a frog egg
In the early 19th century, German zoologist Wilhelm Roux pioneered embryology through frog embryo experiments, where people gradually understood the process of embryonic development, dismantled scientific knowledge, and applied it to modern technology. Ruxian waited for a fertilized frog egg to split into two cells, and then poked one of the cells with a hot needle, so he could know if each cell had its own use to form an embryo, or if only one of the cells was needed. As a result, the cell punctured by the hot needle did not continue to divide, and the intact cell divided all the way to the early embryo, but only developed into half an embryo. This experiment proved that the punctured cell is also the key to embryonic formation, and that when it divides into two cells, the work of each cell has been distributed. William Lew therefore proposed the Mosaic Theory, which believed that each cell would only differentiate into designated somatic cells at the early stage of division, rather than at a later stage.
Half of the frog eggs poked by the needle did not develop, while the other half that was not destroyed developed into only half an embryo
An experiment to cut sea urchins
In 1890, a German biologist, Hans Driesch, objected. He separated the four cells as the sea urchin embryo split into four cells, with the result that each cell developed into a separate intact sea urchin. According to Lu's previous theory, each cell should develop into a different part of the urchin, because each cell has been designated early in embryonic division to differentiate into which part of the urchin. But Durichol's opposite experiment gave a different answer. He believes that cells are not assigned work at first, only divide, and do not differentiate until later stages. So whose conclusion is correct?
Who would have thought a baby sea urchin would look like this Source: Boston University
An experiment to divide salamanders
To unravel the mystery, another German embryologist, Hans Spemann, tied a knot in the middle of a salamander egg with his hair, one half with a nucleus and the other without a nucleus. As a result, half of the nucleus has been dividing, while the half without the nucleus remains unchanged. When the nucleus half divides into sixteen cells, loosen the middle knot, release one of the cells to the half that originally had no nucleus, and finally the salamander egg hatches two small salamanders. This experiment shows that until the embryo divides into sixteen cells, each cell's task has not been assigned, and it still has the ability to differentiate into any special cell. That is, only one embryonic cell is needed to develop into a complete individual.
Another awesome frog experiment
In 1960, John Gurdon also made another experiment with frogs, for which he won the 2012 Nobel Prize in Medicine. He extracted the egg of a female green frog and destroyed the nucleus of this egg with ultraviolet light, leaving the rest of the egg. He then extracted the nucleus of an intestinal cell from an albino frog and injected it into an egg that had been damaged by ultraviolet rays. The small tadpoles that hatch in the end all develop into albino frogs, that is, the same species as the frog that provides the nucleus. Because intestinal cells are differentiated cells, and intestinal cells can also clone an individual, this proves that cell differentiation does not reduce genetic information, but selects which gene is activated.
A group of cloned white frogs
Finally it was Dolly's turn
In this way, after more than a hundred years of scientific practice, Dolly was born. In a similar way to Gordon, an egg was extracted from the ovaries of Scottish Blackface and the nucleus was removed. Mammary cells were extracted from the mammary glands of the Finnish Dorset sheep, and after injecting these breast cells into eggs with the nucleus removed, they were placed in the womb of the Scottish blackface sheep, which became Dolly's surrogate mother. From the previous frog experiments, we know who provides the nucleus, and the final offspring will look the same as the one who provides the nucleus, so of course, Dolly looks the same as the Finnish Dorset sheep.
Dolly has spent her entire life at The Roslin Institute, living a normal life like any other sheep. She also successfully conceived six lambs. It wasn't until 2003 that a veterinarian discovered a tumor in Dolly's lung through a CT scan and decided to administer euphoria to end her pain.
After Dolly's death, the Rosslyn Institute donated her remains to the National Museum of Scotland in Edinburgh in Edinburgh, where she became one of the museum's most popular exhibits. The birth of Dolly shocked the world because it was the first mammal to develop from somatic cells and a milestone in cloning technology.
Clone Dolly the Sheep
Ferret! Ferret! Ferret!
Nowadays, cloning technology is a fairly mature science and technology. In December 2021, the United States successfully extracted cells from an endangered animal that had died for 30 years, the Black-footed Ferret, and cloned a baby ferret. In fact, behind every small scientific progress there are thousands of scientists who have worked hard for it, and while thanking science and technology for bringing great changes to our lives, we must not forget those scientists who have struggled.
Cute black-footed ferret Source: Smithsonian Institution