Animal clones have significant behavioral and physical differences.
Translated from the Greek word "klon" means "twig stalk, escape" and is directly related to vegetative reproduction. Cloning of plants by cuttings, buds and tubers familiar to gardeners for more than 4 thousand years. Since the 70s of last century, for the cloning of plants began to use even individual somatic (asexual) cells.
Can the special conditions to reproduce genetically replica of any living being? The symbol of the first cloned mammal (1996) was the sheep Dolly, who suffered during the life of pneumonia and arthritis and forcibly putting to sleep at the age of six years old — age, equal to about half the average life of a normal sheep. Cloning of animals was not so easy to implement, as plants.
Actually the cloning process can be divided into several stages. At first, a female egg cell is taken from a microscopic pipette pulled her core. In a nuclear-free egg injected another containing the cloned DNA of the organism. Since the merge of new genetic material from the egg, is expected to begin the process of cell reproduction and growth of the embryo. These expectations were based on at least two distinct scientific motivations. The first is the desire to find out how much remains intact genetic material in the process of development of the organism, which has a characteristic fate. The second motivation is that, as far as the factors most egg cytoplasm compatible with the introduction of it to reprogram the genetic material — for example, does it matter that other people's genes and the genes of the mitochondria own egg different? There is a lot of similar questions. Let us turn to the history of research attempts to clone animals.
The history of the appropriate year to date in 1839, when Theodor Schwann cell theory proved to be enshrined in the biology textbooks in the following slogan: the cell is derived from the cell. Cell theory is fraught with two contradictory beginning heredity and differentiation. Whether formed as a result of cell division two identical daughter cells or derivatives of different? In 1888, William Rowe tried to answer this question, a hot needle destroying the two-cell frog embryo. Experience Rowe was unsuccessful, but a second attempt Hans Dreysha in 1892 to split the two and even four-cell sea urchin embryo into individual cells failed: each of the separated cells grown in normal larva. Similar results were obtained a few years later and the other scientists. One of them was Hans Spiman which divided in 1901 amphibian embryos and grow the cells of the child well-functioning tadpoles. However, some invertebrates, including nematodes, showed more regulatory than the mosaic development — after cell division had a different fate.
When the carrier of heredity identify carriers of chromosome core, scientific attention has shifted from the cell to the nuclear potential. In further studies Spiman already experimented with transplanting nuclei of amphibians, and sea urchins. He pulled one of the cores 16 cell embryo and placed it into the germ cytoplasm. The merger was the start of a normal embryo. Thus, it was demonstrated that the potential core remains unchanged at least until stage 16 cells. Spiman seriously thinking about the experiment, when he will be able to transplant the egg cell nucleus single adult, but for such "non-traumatic" operations over the cells he had neither the time nor the technical possibilities.
The time has come after the Second World War, in 1952, when the Americans Robert Briggs and Thomas King rocked the scientific world the message about the successful nuclear transfer frog Rana pipiens. The nuclei were removed from the undifferentiated cells of the blastula — they are transplanted into unfertilized eggs with a remote genetic content. Once the eggs have been stimulated by the development of which grew the normal tadpoles. However, when the nuclei were removed from the gastrula (following the blastula stage of division), the proportion of surviving larvae markedly decreased. A nucleus of the later period of development in general have failed recovery. By 1960, Briggs and King came to the disappointing conclusion that differentiation is accompanied by the progressive narrowing of the possibility of nuclear stimulate the normal development of the organism.
At the same time in England Swedish embryologist Michael Fishberg and colleagues Elsdeylom Thomas and John Gourdon worked overlooking the frog Xenopus laevis, more promising for research than Rana, since it is easier addressed issues of transplantation. On the example of udals Xenopus tadpoles grow from the nuclei of mature individuals. It was a real breakthrough. However, the continued hard work, Gourdon found that the nucleus of the later stages may develop into an adult with a lower probability than the blastula of 30% for the late embryonic stages, and 6% for the newborn tadpoles and 3% for actively swimming forms. What has caused this change, cell differentiation, or the terms of transplant?
With the accumulation of knowledge and the development of experimental techniques have become more accurate and valid. In 1967, Maria Di Bernardino and King declared more than 1,200 nuclear transfer Rana, taken from the differentiated neural cells. Only four cases were transplanted normal chromosomes, and three of them were in the development bias. Bernardino and King concluded that the observed abnormal development of their chromosomes and the deviation from the norm was the result of transplantation. To adapt to the new core cytoplasmic conditions Bernardino decided transplanting them into oocytes, but not in mature gametes. In late 1983 Hofner Bernardino and Nancy have shown that transplanted into the oocyte nucleus of adult blood cells can develop to the tadpole stage. The same core, but transplanted to the eggs have not progressed beyond the early gastrula.
On the example of Xenopus Gourdon and colleagues eventually learned to create a fertile adult frogs, using the core of individual epithelial cells of the digestive tract of tadpoles. This meant that used to be transplanted genetic material still contained the necessary information for the whole body. Despite the impressive results, grow a full amphibian by transplanting mature nucleus into an egg, or oocyte has not succeeded.
Along with amphibians and conducted experiments on mammals. In 1942 were obtained from rats live isolated in step 2 blastomere cell division, and in 1968 — from rabbits to divide into 8 squares. Following earlier attempts to induce fusion of somatic cells with the virus, Bromholl received a microsurgical technique blastocyst injection core embiriona early in the rabbit egg with remote kernels, and Yukio Tsonuda introduced genetically labeled nuclei into fertilized mouse eggs: the development phase lasted until the blastocyst stage, if the core were taken of morula or blastocyst inner cell mass.
The first application for live mice after nuclear transfer Ilmensi belongs to Charles and Peter Hoppe. However, their results have not been repeated — a condition required for the scientific evidence — despite the determined efforts of James McGrath and Davor Salter get pups from nuclear transfer to mouse unfertilized eggs. Success accompanied researchers at the single cell stage, using the induction with virus, but taken at a later stage core unable to initiate development.
In 1979, Steen Villandsen raised some adult cells from embryos vosmikletochnyh sheep and cattle. In his experiments, he adopted the potential economic benefits to be gained from the breed with good genetic material. Ironically, the experiments on nuclear transplantation in cattle have been more effective than in mice. In 1991 Villandsen informed about the experiment on the transfer of nuclei 100 calves, the source of which was a morula. The result of these experiments were clones of the eight calves received their embryos from one donor. Unfortunately, all of the calves developed with disabilities and had obvious signs of pathology.
Ian Wilmut of the Roslin Institute of Scotland looking for a more effective way of genetically modifying the genetic material of sheep and cattle, rather than blind introduction of the nuclei into the egg. In his experiments he used exclusively for transplant stem cells from mice of the inner layer of a blastocyst. Wilmut colleague Keith Campbell was struck by retaining their core capacities division even in differentiated cells. The scientists were convinced that the secret of a successful transfer of genetic material is in the synchronization of cell cycles of donor and recipient. They were the first to attempt to recreate the undifferentiated stem cells of sheep, though at first they were pursued by continuous failures. To increase the likelihood of success, they kept the cultured cells at rest — to align donor cell cycles and unfertilized egg. After a pause, to start the process of embryonic pacemaker was used. As a result of manipulation of samples 244 34 developed to the stage where they could be implanted into the uterus of a surrogate mother. In the summer of 1995 five lambs were born, two of whom — Megan and Morag, the first cloned mammal — lived up of mature age, but then did not learn of the mission entrusted to them.
However, Wilmut and Campbell were not going to stop there. In addition experiments nuclear transfer embryonic stem cells, researchers used kernel cultured fetal fibroblast cell culture giving a constant chromosome. They also studied the nuclei of cells cultured mammary glands 6-year-old sheep. So began to appear in the light of the cloned sheep. Dolly was the only survivor out of 277, but this procedure is now increasingly used in cloning goats, mice, and calves (survival of approximately 3%). Many die after implantation in the uterus, the other — as a result of developmental abnormalities. Scientists believe that the reason for that — incomplete reprogramming of the genetic material.
The task of creating elite breeds of farm animals promotes research on cloning in this area. Cloning by cell migration is increasingly being used for replication and close home. Many people would like to clone their pets — cats and dogs. A California millionaire financed research project «Missiplicity Project», which aims to clone his beloved dog Missy. However, the genetic identity does not mean the repetition of character and temperament clone. Creator of the world's first cloned cat Cc (born Carbon copy — printed with carbon) of Duane Kraemer & M University in Texas notes that C can not be fully considered as a copy of the "grandparent" Rainbow: it is more inquisitive and playful than Rainbow. In addition to temperament, Cc is different from the color of the Rainbow.
Significant differences were noted clones, and other scientists. Pig-clone named Glutton gladly eats everything and runs on anything that moves, while her sister cloned fastidious turn up his nose from the orange and kicking when it is taken in his hands. Moreover, the clones are considerable differences in the physical density and the number of teeth wool. An attempt by Robert Lanza, of the Massachusetts Institute of Technology in Worcester clone a monkey, an alcoholic named Buttercup, so still did not succeed. Scientists, however, do not despair and continue to study.
People — animals too, so experiment with "smaller brothers" are a model for humans. Reproductive cloning, in which a human embryo from a somatic cell is implanted into the uterus, it is forbidden by law in many countries. The more the number of deaths and malformations in the reproductive cloning of mice and farm animals make this technology unsuitable for human now. However, even if one day technology will be effective, people can not avoid a number of social and ethical issues.
The fact that the man is too complex for being over him manipulation of cloning, according to data from the real medicine to study the normal development of the fetus in the womb. The figure presents a simplified inborn errors of morphogenesis:
According to the international classification of all birth defects are classified into 4 groups: congenital malformations, dizruptsii, and dysplasia.
Congenital malformation — morphological or anatomical defect in the body of the organ or area of the body as a result of genetically determined violations of embryonic differentiation.
Deformation — anatomical abnormality shape or position of a body or body parts by mechanical effects on the fetus without violations of embryonic differentiation.
Dizruptsiya — morphological or anatomical defect in the body of the organ or area of the body as a result of externally sredovye effects on fetal development.
Dysplasia — morphological defect of cells or tissue structures as a result of genetically determined violations of differentiation of cells or tissues.
Isolated congenital malformations usually do not cause any difficulties in the diagnosis and surgical treatment as the modern pediatric surgery has tremendous experience in the treatment of many pathological states of this type. As for the multiple birth defects, then to them the experience and knowledge of the diagnosis and treatment of isolated congenital defects are applicable only to a limited extent or not applicable at all.
From about mid-50s needs of clinical practice contributed to the expansion of research to study the etiology and pathogenesis of multiple birth defects. It was in the 50s in clinical medicine began to form an extensive section, later named sindromologiey. Probably the beginning of its appearance can be regarded as the appearance of the famous encyclopedia Laybera and Olbrich "Dictionary of Clinical Syndromes" (Urban and Schwarzenberg, Munich, 1957), which described hundreds of syndromes and their synonyms, and in subsequent editions of this encyclopedia analyzed the etiology, pathogenesis and modern nomenclature of these states. With the development of the techniques of modern medicine and genetics have already described hundreds of new syndromic forms of human pathology. A well-known catalog Mac Cusick in electronic form on the Internet has more than 5000 normal and pathological features of a person inherits according to Mendel's law, and the number of these signs of increasing monthly. The famous London sindromologii database currently has more than 2,500 syndromes, and every year in periodicals 10-20 describes the "new" clinical entities syndromic human pathology, and, apparently, that the process of describing the "new" syndromes endless. By the early 80-ies of the amount of information in this area has become so large and diverse that it took the unification of modern terminology, concerning the definition of syndromes and similar forms of multiple lesions of the human body.
Thus, the idea of getting "identical human clone" is so unworkable and mythological in nature, it is better to write the epitaph on her monument, than to engage knowingly false fabrications. In any case, in the foreseeable future.