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The genetic (of the Greek genno γεννώ = to give birth) is the Science which studies the chemical functions inherent in a particular species of molecules called Gène. One of its branches, the formal genetics or mendélienne, is interested in the transmission of the hereditary characters between parents and their descent. This term gathers a big number of disciplines, the majority associated with the Biologie.

History

The study of the transmission of the characters to the descent was already practiced by the stockbreeders, and it is considered that the various races of Chien S ( Canis familiaris ) have come from successive selections of wolf S ( Canis lupus ) for 20.000 years (it was shown that these two species of Canis are interfécondes). Interpretation starting from a unit which is the gene is more recent (see the Chronologie). Lamarck carried out experiments to include/understand if the acquired features were transmitted of one generation to the other. Louis Pasteur, by proving the absence of spontaneous Generation, establishes that an living being has at least an ancestor from which it draws his characteristics. The first serious study on the subject is carried out by the monk Gregor Mendel, considered as pioneer of the genetics. By observing the transmission of the morphological characteristics of Pea through some generations, it defines the terms of Phénotype and Génotype and it states, by giving a small nudge in the right direction to its figures, the laws known as of Mendel, bases modern genetics, and this, well before the discovery of DNA. August Weismann postulated in 1883 the existence of a material support of heredity. This theory then defended the impossibility of the transmission of the acquired features (neolamarckism) and required a full adhesion of the Darwinisme:

“ the living beings derive from/to each other by small continuous fortuitous variations screen of the Natural selection . ”

Hugo de Vries in Holland, Carl Correns and Erich von Tschermak in Germany redécouvraient the laws of Mendel at the plants in 1901. In England, William Bateson will become the burning defender of the laws of Mendel, with its book, published in 1902, “ Gregor Mendel' S principle off Heredity ”. Bateson was, moreover the first to be introduced in 1906 the term of genetics. This redécouverte imposed the idea that independent and juxtaposed material particles (called later genes ) were transmitted, according to immutable statistical laws, from generation to generation. The France was at that time, because of its tradition scientific and social lamarckist, well far from accepting such an idea. In 1902 however, the biologist, professor with the Faculty of Science of Nancy, Lucien Cuénot (1866-1951) found these laws in the animal. Then he discovered, in 1905, the first case of lethal gene in the animal, the first phenomenon of epistasy (1907) where several genes located at places different from the Chromosome intervene in the same biochemical way, and, in 1908, the first case of Pléiotropie where certain genes can act on several seemingly independent characters. Between 1908 and 1912, it showed the hereditary origin of certain cases of Cancer. Moreover, since 1903, he proposed a possible interaction between Mnémon (gene), Diastase (Enzyme) and Pigment S (Protéine) what, in the French context of the time, was a prowess. In the United States, Thomas Hunt Morgan and its team developed as of 1910 the chromosomal theory of heredity, starting from the Drosophile, fly of easy breeding and reproduction much faster than the white Souris. He postulated the exchange of chromosomal units during the Méiose and developed a method which made it possible to roughly locate the position of genes on the chromosomes.

Technological advances make it possible little by little to define the concept of gene. It is necessary to await progress of microscopy to locate the support of genes: the Chromosome. In the Years 1950, a new step is crossed by the Americans James Watson and Francis Crick which determines the fine structure of the molecule constituting genes, DNA, and thus helps to include/understand the molecular mechanisms of heredity. A little later, three other Nobel, François Jacob, Andre Lwoff and Jacques Monod, show how this one structure in Codon S to program the protein synthesis starting from Amino-acid, the redundancy of codings, the mechanism of the changes, and the presence of a fine code of of reading , as on a Magnetic band.

Since, the genetic studies make it possible little by little to include/understand the way in which genetic information is coded in the Chromosome S. One also discovered that most of the DNA was not-coding .

More recently, one discovered a heredity based on the DNA mitochondrial. This DNA is at the origin of diseases transmitted exclusively by the mother. Indeed at the time of fecundation, the mitochondries of the paternal Spermatozoïde do not penetrate in the maternal Ovocyte and the mitochondries have (except at very rare exceptions) an exclusively maternal origin.

Various research fields

Very early, the genetics diversified in several different branches:

the genetic of the development studies the molecular actors (and genes which codes them) implied in the formation of the organization starting from the unicellular fertilized egg stage. It is focused particularly on the installation of bilateral symmetry and the mechanisms which make it possible to pass from a simple biological system (unicellular, radiate symmetry) to a complex organization (pluricellular, often metamerized, and built in specialized bodies). It often uses model species to study the mechanisms of formation of the organization (Drosophile, Nématode, Zebrafish, Poulet);

the medical genetic studies the heredity of the human genetic diseases, their segregation in the families of patients. She seeks to identify by this skew the changes responsible for the diseases, in order to develop treatments to look after them;

the genomic studies the structure, the composition and the evolution of the genomes (the totality of the DNA, three billion pairs of bases at the man, organized in chromosomes), and tries to identify reasons in the DNA which can have a biological direction (genes, not translated transcribed units, miRNAs, units of regulations, promoters, CNGs, etc);

the quantitative genetic studies the genetic component explaining the variation of quantitative natures (size, the color of peeling, the speed of growth, concentration of a molecule, etc) and their heritability;

the genetic of the evolution studies the signatures of the natural selection on the genome of the species, and tries to identify the genes which played a crucial role in the adaptation and the survival of the species in changing environments;

the genetic of the populations studies the forces (and their effects) which influence the genetic diversity of the populations and the species (change, drift, selection) by (inter alia) the development of mathematical models and statistical.

The heredity, which studies the Phénotype and tries to determine the subjacent Génotype is always based on the laws of Mendel. Cellular biology and the Molecular biology study the Gène S and their material support (DNA or ARN) within the cell, the cellular Biologie for their expression. Progress of the branch engineering of the genetics, the genetic engineering, could pass the stage of the simple study while making it possible to modify the genome, to establish, remove or modify again genes in living organisms: they are the Organisme genetically modified (GMO). Same progress opened a new way of therapeutic approach: the “genic Therapy”. It is a question of introducing new genes into the organization in order to mitigate a hereditary deficiency.

The unceasingly increasing evolution of knowledge in genetics poses several problems ethical S, related on the Clonage, the various possible types of Eugénisme, on the Intellectual property of genes and the possible environmental risks due to GMO, as it also complicates the comprehension of the operation of the cellular machinery. Indeed, more it is studied, more the actors are numerous (DNA, ARN messenger, of transfer, MicroARN, etc) and the number of feedbacks (épissage, edition, etc) between these actors grows.

Chronology

In 1865 , impassioned natural science, the Austrian monk Gregor Mendel, in the garden of the court of its monastery, decides to work on edible peas presenting seven characters (the shape and color of seed, color of the envelope, etc), of which each one can be found in two different forms. Starting from its experiments, it publishes an article of genetics “Seeks on the vegetable hybrids” where it states the laws of transmission of certain hereditary features. This article is sent to the scientists of the four corners of the world, the reactions are mitigated, even non-existent. It is only in 1907 that its article was recognized and translated into French.

In 1869 DNA is insulated by Friedrich Miescher, a Swiss doctor. It recovers bindings having been used to look after infected wounds and it isolates a substance rich in phosphorus in the pus. It names this substance nucléine. It finds the nucléine in all the cells and the salmon sperm.

In 1879 , Walther Flemming describes for the first time a Mitose. The mitosis had been described already 40 years front by Carl Nageli but that Ci had interpreted the mitosis like an anomaly. Walter Flemming invents the terms Prophase, Métaphase, and Anaphase to describe the cellular division. Its work is published in 1882.

In 1880 , Oskar Hertwig and Eduard Strasburger discover that the fusion of the core of the Ovule and the Spermatozoïde is the essential component of the Fécondation.

In 1900 , redécouverte of the laws of heredity: Hugo de Vries, Carl Correns and Erich von Tschermak-Seysenegg independently redécouvrent the Lois of Mendel.

In 1902 , Walter Sutton observes for the first time a Méiose, proposes the chromosomal theory of the Hérédité, i.e. the Chromosome S would be the supports of the Gène S. He notices that the model of separation of the chromosomes supports the theory of Mendel completely. He publishes his work the same year. Its theory will be shown by work of Thomas Morgan.
The first description of a hereditary human disease by Archibald Garrod: the Alcaptonurie.

In 1909 , Wilhelm Johannsen creates the term Gène and makes the difference between the aspect of a being (Phénotype) and its gene (Génotype). William Bateson, four years front, used the genetic term in an article and the need for naming the hereditary variations.

In 1911 , Thomas Morgan shows the existence of Mutation S, thanks to a Drosophile (fly) Mutant E with the white eyes. It shows that the Chromosome S are the supports of genes, thanks to the discovery of the genetic connections ( genetic linkage ) and of the genetic recombinations. He works with Alfred Sturtevant, Hermann Muller, and Calvin Bridges. He receives the Nobel Prize of Medicine in 1933. Its experiments will make it possible to consolidate the chromosomal theory of heredity.

In 1913 , Morgan and Alfred Sturtevant publish the first Genetic card X chromosome of the Drosophile, showing the order and the succession of genes along the Chromosome.

In 1941 , George Beadle and Edward Tatum put forth the assumption that a gene codes one (and only one) enzyme by studying Neurospora fouled .

In 1943 , diffraction with x-ray of the DNA by William Astbury makes it possible to put forth the first assumption concerning the structure of the molecule: a regular structure and periodical which it describes as a pile of pennies ( like have pile off pennies ).

In 1944 , Oswald Avery, Hake MacLeod, and Maclyn McCarty show that DNA is a Molécule associated with hereditary information and can transform a cell.
Barbara McClintock watch that the genes can move and that the Génome much less static than is provided. It receives the Nobel Prize of Medicine in 1983.

In 1952 , Alfred Hershey and Martha Chase discover that only the DNA of a virus needs to penetrate in a cell to infect it. Their work reinforces the assumption considerably that the genes are made of DNA.

In 1953 , simultaneously to the research tasks of Maurice Wilkins and Rosalind Franklin which carried out a stereotype of a molecule of DNA, James Watson and Francis Crick present the model in double helix of DNA, explaining thus that the genetic Information can be carried by this molecule. Watson, Crick and Wilkins will receive in 1962 the Nobel Prize of medicine for this discovery. In 1955 , Joe Hin Tjio makes the first exact account of the human chromosomes: 46

The April 14th 2003 , the end of the sequencing of the human genome is announced.

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