Gene

History

In the first times of the Genetic , the molecular support of information was completely unknown, but experiments, like work of the monk Gregor Mendel on pea or of Thomas H. Morgan on the flies Drosophile S, could highlight the existence of biological factors of the Hérédité. The transmission of these factors, in the case of simple natures, could be explained by the existence of discrete entities of genetic information: genes.

Later, progress of optical microscopy then techniques of Molecular biology allowed the localization of these genes within the cores of the cell S, the genetic data carrier being long molecules of desoxyribonucleic acid (DNA) called Chromosome S.

Origin of the word : he was proposed by the Danish biologist Wilhelm Johannsen in 1909, at the same time as the terms of “genotype” and “phenotype”. The term resulted from a contraction of the expression of “pangene” forged twenty years earlier per Hugo De Vries. For Vries, the “pangenes” were organoids intracellular, present in all the cells. Johannsen, when it contracted the word “pangene” in that of “gene”, released the concept of any particular morphological interpretation, and proposed to define it in a purely operational way compared to combinative the mendélienne: “It is necessary to treat gene like a unit of counting or calculation. We at all do not have the right to define gene as a morphological structure, within the meaning of the “gemmules” of Darwin, of the “biophores”, the “determinants” or any other morphological kind of concept”.

Definition

Today, a gene is defined like a nucleotide sequence (known as also sequence), i.e. like a desoxyribonucleic portion of acid (DNA), intended to be transcribed in ribonucleic acid (ARN), if it is the case the sequence is known as “coding”. Most of the time, a gene begins with a sequence of Nucléotide S called promoter , whose role is to allow initiation but especially the regulation (all the genes are not expressed in all the cells) of the transcription of the DNA in ARN, and ends in a terminating sequence, which marks the end of the transcription. The molecule of ARN thus produced can either be translated into Protéine (it in this case is called ARN messenger ), or to be directly functional (it is the case for ribosomal ARN or ARN of transfer). There are approximately 13.000 genes in the DNA of the cells of a Drosophile and between 23.000 and 27.000 genes at the Man. An article of May 25th, 2007 published in Science closely connected this number to 20 ' 488, with perhaps a last hundred genes remaining to be discovered.

Fast definition of a gene: Portion of a chromosome which orders the expression of a character precise hériditaire. (hériditaire = which is transmitted from generation to generation). Often, a character is not determined by only one gene but by several. Source of information: deliver 3rd: Ground and life science, edition Bordered.

Form of genes

When a gene is intended to be transcribed in ARN messenger , it contains the necessary information with the synthesis of proteins. At the Eucaryotes, a gene consists of an alternation of sequences coding, called Exon S, and of sequences not coding, the Intron S, which will be eliminated from ARN messenger during the process of épissage, before the translation out of protein. Genetic information is expressed by nucleotide triplets (called Codons), to each codon corresponds an Amino-acid . Some let us code called " let us code STOP" do not have correspondence in amino-acid and define the stop of the translation of the polypeptide ARN. A protein is not nevertheless simply a sequence of amino-acids and its final composition depends on other environmental factors, this is why to a gene necessarily only one protein does not correspond. Moreover, the process of épissage of will introns also allows to remove in a conditional way some exons of the ARN, thus allowing starting from a single gene to produce several different proteins. One speaks then about épissage alternate. This phenomenon initially described for a restricted number of genes seems to relate to a growing number of genes. Today, it is estimated that the alternate épissage makes it possible to produce on average three different ARN by genes, which makes it possible at the human one to produce from its 20.000 to 25.000 genes 100.000 different proteins:

The majority of the cell S of an organization have the totality of genes. The whole of genes expressed in a cell in particular, and thus on the proteins which will be present in this cell, depends on complex ways of regulation set up during the development of the individual. Certain simple characters are determined by only one gene (as the blood group at the man or like the color of the eyes at the Drosophile). However, in the majority of the cases, an observable character depends on many genes and possibly on the interaction with the environment (the shape of the face, weight of the body).

It should be noted that if the genes are the principal persons in charge of the variations between individuals, they are not the only information support in an organization. Thus, it is considered that in the case of a great number of organizations a good part of the DNA is not coding (only 3% are coding at the man), remainder (the DNA not coding) having functions still badly known. This DNA not coding, also called DNA intergenic, is studied more and more, and seems to be implied in the structure of the Chromatine. More particularly, last research showed a crucial role of these areas in the regulation of the form of the genes by modification of the state of chromatin on great chromosomal areas.

Egoistic gene

In its work the egoistic gene , Richard Dawkins exposes in 1976 a theory giving to gene the role of unit on which the Natural selection acts (a role usually reserved for the individual). The individuals would have of another interest only to ensure the transmission of the genes which they carry (an idea which gives its title to the book the misadventures of the gene of Pierre-Henri Gouyon, Jean-Pierre Henry and Jacques Arnould). It can exist conflicts between the level of gene and that of the individual: the genes carried by the fraction of the genome transmitted by the female way may find it beneficial to produce more descendant females and to handle the individual who carry them in this direction, for which it is more favorable in the majority of the cases to produce as many males as females. The concept of gene egoistic approaches in fact the concept of Sélection of parentèle in that the gene which dictates an altruistic act for the benefit of another related individual supports in fact its own transmission.

Types of genes and technical vocabulary

The term of gene is so broad that it is sometimes difficult to give a definition of it. Many derivatives, with the direction much more precise, and sometimes technique, are usually used in the scientific circle.

Gene with zygotic action : gene which is expressed only at the zygote and which is not a maternal contribution to the ovocyte.

Gene (S) activating recombination (RAG) : (RAG; Recombination Activating Genoa): together of genes coding of the proteins which play a fundamental role in the rearrangement of other genes. For example, genes RAG-1 and RAG-2 code proteins which activate the rearrangement of antigenic genes of receivers.

Gene (S) for maternal purpose : (Maternal-Effect Gene) gene with maternal expression; maternal gene whose products of expression in the cytoplasm of the ovule support the development of the future embryo; this gene contributes to the phenotype of the descendant according to its expression in the mother.

Gene architect : gene which controls the embryonic development.

Gene antisens : gene which produces a ARN m complementary to transcribed of a normal gene, generally built by inverting the area coding compared to the promoter.

Gene candidate : the approach gene candidate consists in supposing the implication of a gene in any effect a priori, and the study aims at confirming this implication a posteriori.

Gene positional candidate : gene known to be localized near a marker of DNA related to a character controlled by only one Locus or on a QTL (locus for quantitative purposes), and from which the function deduced suggests that it can be the source of the genetic variation of the character in question.

Gene positional candidate by compared cartography : refers to an indirect means to allot a function to a QTL. When a QTL is related to a marker for a species, and that this same marker is related to a gene known in a model species, predictions can be made concerning the nature of QTL.

Gene dream or gene of fusion : gene modified genetically, obtained when a coding sequence is amalgamated with a Promoteur and/or other sequences derived from a different gene. The majority of genes used in the transformation are chimerical.

Gene dream marker of selection : gene manufactured starting from pieces of two or several different genes and which makes it possible the host cell to survive under conditions which, otherwise, would result in its death.

constitutive Gene : gene which is always expressed (without mechanism of regulation); i.e. a gene of maintenance (gene of household; domestic gene or housekeeping embarrassment); gene expressing same manner in all the cells of an organization; the product of expression of this gene is essential to the life of the cell (with its basal metabolism). Very often, these genes do not have a box TOUCHED.

Gene of anchoring : gene which was localized on the physical chart and the chart of connection of a chromosome, and thus allowing their mutual alignment.

Gene of avirulence or gene avr : several plants contain genes R which confer a resistance to simple heredity on a specific race of pathogenic. The plants are able to recognize the presence of pathogenic by an interaction between their gene R and corresponding gene of avirulence of the pathogenic one. The successful recognition starts activation in cascade of new genes, often leading to a hypersensitive Réponse.

noxious Gene : gene whose deterioration (following a change, for example) involves a problem on the level of its expression, which leads to the appearance of an abnormal phenotypical nature.

Gene of histocompatibility : together of genes which code the antigens of the Major Complex of Histocompatibilité (CMH).

Gene of interest : (transgene): gene coding a protein of interest; this gene is introduced in experiments into an organization (which becomes an organization genetically modified or GMO or organization transgenic) so that this last produces protein in question.

segmentary Gene of polarity : gene which functions to define the former and posterior components segments of the body in the Drosophila.

Gene of the organoids : genes located in the Organoid S apart from the core.

Gene interrupter : employee to reinforce the sterility of seeds obtained starting from the genetically modified cultures.

fragmented Gene : at the eucaryotes, the DNA coding several structural genes is composed of exons and of will introns. This model of interruption generally found in the coding sequence is indicated under the name of “fragmented gene”.

Gene gus : gene of E. coli which codes the bétaglucuronidase (GUS). Since this activity is absent at the plants, this gene is generally used as gene rapporteur to detect the occurrence of the events of transformation.

Gene hémizygote : gene which is present only in only one copy in an organization diploïde (one can quote like example genes related to X chromosome in the mammals of male sex).

early immediate Gene : viral gene expressed immediately after the infection.

inductible Gene : gene which is expressed only in the presence of one specific metabolite, the inductor.

lethal Gene : the mutant shape of a gene, fatal with the state homozygote.

recessive lethal Gene : gene coding a protein which is necessary for the passage of the organization to the adult state. If the two alleles of this gene are present at the recessive state, the fetus has problems to develop; he dies in the birth or shortly after.

dependant Gene or dependant marker : gene or marker related to another gene or marker.

Gene marker : gene whose function or position is known, used in the selection assisted by markers (SAM) or in the genetic studies.

Gene marker of resistance to the antibiotics (ARMG for antibiotic resistance marker embarrassment ): genes generally of bacterial origin used as markers of selection in transgenèse, because their presence allows the survival of the cells in the presence of normally toxic antibiotic agents. These genes were used in the development and the release of the first generation of organizations transgenic (particularly at the crop plants), but they are not recommended any more because of the possible hazards associated with the transfer nondesired with resistance to antibiotics at other organizations.

modifying Gene : gene which affects the expression of some other genes.

mutable Gene : gene which has a frequency of exceptionally high change.

orphan Gene : gene or sequence of DNA whose function is not known.

Gene by : classify genes necessary to the faithful segregation of the plasmide during the cellular division. Initially, the loci by were identified in the plasmides, but later, they were also found in the bacterial chromosomes.

Gene (S) paralogist (S) : genes having evolved/moved starting from the duplication of the same starting gene.

polymorphic Gene (polymorphic embarrassment): existing gene in several forms (various allelic forms).

Gene rapporteur : gene coding an easily analyzable substance. Used as marker to confirm the incorporation of a transgene in a cell, a body or a fabric, and as a means of examining the effectiveness of specific promoters.

regulating Gene : gene whose primary function is to control the rate of synthesis of the products of one or several other genes or ways.

repressible Gene : gene whose expression can be reduced or destroyed by the presence of a regulating molecule.

jumping Gene or element transposable or transposon : element of DNA which can move of a place to another in the Génome.

structural Gene : gene coding a polypeptide which has enzymatic or structural functions and which is necessary for the normal metabolism and the growth of a cell or an organization.

Gene suppressor of tumor : gene which regulates the cell multiplication. If such a gene becomes nonfunctional and the cell sudden a deterioration, then a not-controlled growth or a cancer could result from it.

additive Genes : genes of which the Net effect is the sum of the individual effects of their Allèle S, they present neither predominance nor epistasy.

complementary Genes : two or several interdependent genes, for which (in the case of dominant complementarity) the allele dominating of the one of them can produce an effect on the phenotype of an organization only if the allele dominating of second gene is present; in the case of recessive complementarity, only the double individuals homozygotes recessive can express the effect.

cytoplasmic Genes : genes located on the DNA apart from the core, i.e. in the plastids and the mitochondries.

Genes of segmentary parity : gene which influences the formation of the segments of the body in the Drosophila.

piled up Genes : refers to the insertion of two or several genes in the genome of an organization. An example would be a plant carrying a transgene LT giving resistance to an insect and a transgene bar giving resistance to a specific weedkiller.

Genes extranucléaires : genes which are elsewhere than in the core (e.g.: in the mitochondries, plastids).

Genes homeotic : genes acting harmonizes some to determine the fundamental models of development.

Genes R : classify vegetable genes which confer resistance to a specific strain (or a whole of stocks) of a pathogenic private individual. Their primary function is to detect the presence of pathogenic and to start the ways of defense of the plant. Genes R were clones starting from a certain number of plant species.

Genes rol : family of genes present on plasmide IH of Agrobacterium rhizogenes, which induces the formation of roots when they are transferred to a plant, following an infection by the bacterium. These genes are used like a means of induction racinaire at various species and cultivars of micropropagés fruit trees.

Genes to vir : together of genes on a plasmide Ti or IH which prepare the segment of ADN-T for the transfer in a vegetable cell.

Pseudogène S : together of genes which in consequence of modification of its sequence, cannot be any more transcribed in ARN and/or translated into proteins. They are not expressed genes.

major Genes :

Genes modulator :

Nomenclature of localization of a gene

the localization of a Gène is founded on a standard model of clear and dark bands obtained after application of a technique of coloring.
the gene is initially located by the number of the chromosome for the nonsexual chromosomes (1 to 22) and by a letter (X or Y) for the sexual chromosomes.
a letter follows the designation of the chromosome, p (indicating the small arm of the chromosome) or Q (indicating the large arm of the chromosome).
the localization is obtained by the two following numbers which represent the area and a band. More the number indicating the area is large plus it is far away from the centromère (the point of meeting of the arms of the chromosome).
Enfin there exists sometimes a point followed of one or two digits representing a sub-band.

The genes homeotic control the embryonic development. the genes are located in the DNA which is a macromolecule contained in the chromosomes which are contained in the core of the cell.

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