Cloning is usually artificially induced asexual reproduction or natural asexual reproduction (such as plants). Cloning is a multicellular organism, genetically identical to another organism. Clones can be natural clones, such as asexual reproduction or individuals with identical genes (just like identical twins). But what we usually mean by cloning is an identical copy produced by conscious design.
The cloned English word "clone" comes from the Greek word "kl! N "(twig). In horticulture, the word "clone" was used until the 20th century. Later, sometimes "e" is added to the end of the word to become "clone" to indicate that the pronunciation of "o" is a long vowel. Recently, with the widespread use of this concept and word in public life, spelling has been limited to the use of "cloning". The Chinese translation of this word is transliterated as "clone" in Chinese mainland, but it is often translated as "copy" in Hong Kong and Taiwan. The former "clone" is like the transliteration "copy" of copy, which has the disadvantage of not looking at the meaning of the text; The latter "copy" can roughly express the meaning of cloning, but it is inaccurate and easy to misunderstand.
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 one individual (for example, by PCR), then inserting it into another individual (usually by vector), and then studying or utilizing it. Cloning sometimes refers to the successful identification of a gene with a certain phenotype. So when a biologist says that the gene of a disease has been cloned successfully, that is to say, the position and DNA sequence of this gene have been determined. Obtaining a copy of this gene can be considered as a by-product of identifying this gene.
Cloning an organism means creating a new object with exactly the same genetic information as the original organism. Under the background of modern biology, this usually includes somatic cell nuclear transfer. In somatic cell nuclear transfer, the nucleus of oocytes is removed and replaced by the nucleus taken from cloned organisms. Usually, oocytes and their transplanted nuclei should come from the same species. Because the nucleus contains almost all the genetic information of life, the host oocyte will develop into an organism genetically the same as the nuclear donor. Although mitochondrial DNA has not been transplanted here, it is still relatively rare, and its impact on organisms can usually be ignored.
In horticulture, cloning refers to the offspring of a single plant produced by vegetative propagation. Many plants obtain a large number of offspring from one plant by cloning this asexual reproduction.
Cloning progress
Modern cloning techniques, including nuclear transfer, have been successfully tested in some species (in chronological order):
Frog: 1962, unsuccessful.
Carp: 1963, China scientist Tong Dizhou successfully cloned a female carp by inserting the DNA of a male carp into the egg of a female carp as early as 1963, which was 33 years earlier than Dolly's cloning. However, because the related papers were published in a China sci-tech journal and were not translated into English, they are not well-known internationally. (From: Public Broadcasting Company)
Sheep: 1996, 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.
Dog: 2005, experimental team of Seoul National University, South Korea, Snaby.
Although great progress has been made in cloning research, the success rate of cloning is still quite low: before Dolly was born, researchers experienced 276 failed attempts; After 9000 attempts, 70 calves were born, and one third of them died at an early age. Prometea also made 328 attempts to be born successfully. For some species, such as cats and orangutans, there are no reports of successful cloning. The cloning experiment of dogs is also the result of hundreds of repeated experiments.
Dolly's age test after birth showed that she was old when she was born. At the age of six, she developed arthritis, which is common in old age. This aging is thought to be caused by the wear of telomeres. Telomeres are terminal chromosomes. With cell division, telomeres are constantly worn during replication, which is usually considered as the cause of aging. However, after successfully cloning cows, the researchers found that they were actually younger. The analysis of their telomeres shows that they not only return to the length at birth, but also are longer than the telomeres at birth. This means that they can live longer than ordinary cattle, but many of them die prematurely because of overgrowth. Researchers believe that related research can eventually be used to change human life span.
Human cloning
Because of the possible ethical and practical consequences, human cloning has always been a controversial topic. Many people think it is immoral to try to clone human beings, but some scientists openly claim to try to clone human beings. Some groups claim that they are conducting human cloning research or have cloned people, but there is no independent source to confirm this.