One of the main problems faced by cloning technology is the low fertility rate of cloned animals. The more reproductive generations, the lower the fertility rate. So far, the limit has been reached when the experimental mice breed for six generations and the cattle breed for two generations. Once the animal that provides cells for cloning dies, the genetic information will be cut off.
In 2005, a research team led by Wakayama Mingyan, a researcher at the Institute of Physical and Chemical Research, found that when breeding cloned experimental mice, soaking the eggs with transplanted nuclei in a kind of "histone deacetylation 5" called "Qugu bacteriocin A" would improve the fertilization rate. The research team continuously improved the technology and successfully bred 26 generations of experimental mice, with the highest fertilization rate of about 15%.
A research team of Oregon Health and Science University published an article in the online edition of the American science magazine Cell on June 5438+05, announcing that the cell nucleus of other people's skin cells had been implanted into egg cells by using the "somatic cell cloning technology", and successfully produced embryonic stem cells that could differentiate into various tissues for the first time. In biology, cloning is usually used in two aspects: cloning a gene or cloning a species. Cloning a gene refers to obtaining a gene from an individual (for example, by PCR) and then inserting it. In addition, there are also asexual reproduction in the animal kingdom, but it is more common in invertebrates, such as the division and reproduction of protozoa and the budding and reproduction of caudate animals. But for advanced animals, under natural conditions, they can only reproduce sexually, so scientists must go through a series of complicated operating procedures to make them reproduce asexually. In 1950s, scientists successfully cloned the amphibian Xenopus laevis, which opened a new chapter in cell biology.
In the late 1980s, Britain and China successively used embryonic cells as donors to "clone" mammals. By the mid-1990s, China had cloned five kinds of mammals, including mice, rabbits, goats, cows and pigs. 1On July 5, 1996, a lamb named Dolly was cloned, and its genetic structure was exactly the same as that of the donor, which caused an uproar in the world. Dolly is special in that her life was born without the participation of sperm. The researchers first sucked genetic material from a sheep's egg cell and turned it into an empty shell, then took out breast cells from a 6-year-old ewe and injected genetic material into the empty shell of the egg cell. In this way, an egg cell containing new genetic material but not refined was obtained. This modified egg cell divides and proliferates to form an embryo, which is then implanted into the uterus of another ewe. With the smooth delivery of ewes, "Dolly" came into this world.
But why don't other cloned animals have such great influence in the world? This is because the genetic genes of other cloned animals come from embryos, and they are all nuclear transplants with embryonic cells, which cannot be strictly said to be "asexual reproduction". Another reason is that the embryonic cell itself is sexually propagated, and the genome in its nucleus is half from the father and half from the mother. Dolly's genome comes from a single parent, which is really asexual reproduction. Therefore, strictly speaking, "Dolly" is the first truly cloned mammal in the world. 1On February 23rd, 997, scientists from Roslin Institute in Scotland announced that their research team had successfully cloned goats from somatic cells. Cloning technology is the result of scientific development and has a very broad application prospect. In horticulture and animal husbandry, cloning technology is an ideal means to cultivate varieties with stable genetic traits, and high-quality fruit trees and improved livestock can be cultivated through cloning technology. In the medical field, the United States, Switzerland and other countries have been able to use "cloning" technology to cultivate human skin for skin grafting. This new achievement avoids the possible rejection of allogeneic transplantation and brings good news to patients. According to China Xinhua News Agency1April 4, 1997, Cao Yilin, an expert in plastic surgery in Shanghai Ninth Staff Hospital, successfully cloned human ears in mice for the first time in the world, bringing hope for the repair and reconstruction of missing organs. Cloning technology can also be used to breed many valuable genes, such as insulin for treating diabetes, growth hormone that is expected to make dwarfism patients grow taller again, and interferon that can resist many diseases and infections.
Cloning is a major technological breakthrough in the field of biological sciences, which reflects the progress of nuclear differentiation technology, cell culture and control technology. Originally, it was a transliteration of English clone, which means the offspring individual population with the same genotype formed by biological cell asexual reproduction, referred to as "asexual reproduction". The great breakthrough of animal cloning technology has also brought widespread controversy. Sheep: 1997, Dolly
Macaque: Tetra, female, June 5438 +2000 10.
Pigs: in March 2000, 5 Scottish PPL piglets; August, Xena, female
Cattle: 200 1 year, alpha and beta, male.
Cat: 200 1 ending, plagiarist (CC), female.
Mouse: In 2002.
Rabbit: It was independently realized in France and South Korea from March to April, 2003;
Mule: May 2003, Gem, Idaho, male; June, Utah pioneer, male
Deer: Dewey in 2003.
Ma: Prometea, female, 2003; Italian scientist
Dog: Snoopy, Experimental Team of Seoul National University, Korea, 2005.
Pigs: On August 8, 2005, the first pig cloned from donor cells in China.