Gene
A gene is organized linear sequence of nucleotides in the molecule of DNA (or RNA for some viruses), which contains the information necessary for the synthesis of a macromolecule with specific cellular function, usually proteins, but also mRNA, ribosomal RNA , transfer RNA and small RNAs. 
Schematic diagram of a short gene, within the double helix structure of DNA which when compressed will form a chromosome (right). It is a eukaryotic gene (the prokaryote lacks introns). The proteins are encoded only in the exons.
This function can be linked to the development or operation of a physiological function. The gene is considered as the unit of genetic information storage unit inheritance to transmit this information to the offspring. The genes are arranged, then, along both chromatids of the chromosomes on chromosome occupies a specific position called locus. The set of genes from one species, and therefore of the chromosomes that make them up, called genome.
History
The concept of gene has been changing over time, as science has progressed which studies the genetics:
Gregor Mendel in his experiments proposed the original idea of the gene, although it's not called genes, but factors that would come to be responsible for the transmission of characteristics from parents to children (what is now called genotype). Mendelian gene is a unit of function, structure, transmission, mutation and evolution that is orderly and linearly distributed in the chromosomes.
The word gene was coined in 1909 by Danish botanist Wilhelm Ludwig Johannsen from a Greek word meaning "generate", referring to the physical and functional unit of heredity.
By 1950, won the concept of gene as the DNA strand that directs the synthesis of a protein. This is a concept that provides a molecular or structural nature to the gene. The gene encodes a protein and must have a structure defined by the linear order of their triplets.
Later comes the concept of gene as "the DNA strand capable of directing the synthesis of a polypeptide. This concept comes to see that the majority of proteins are formed by more than one polypeptide chain and that each is encoded by a different gene.
We now know that some genes encode more than one polypeptide and a protein can be encoded by the set of different genes. The existence of overlapping genes and processing alternative dispute the hypothesis of a gene -> a polypeptide. Rather it should aim to reverse relationship, a polypeptide -> a gene. There are also some genes that do not encode proteins but RNA with specific function (transfer RNA and ribosomal RNA, for example) and which are not translated, so no translation is required for a gene has a specific function. The gene is thus the smallest unit of genetic function that can be inherited.
Types of genes
A gene is a sequence or segment of DNA required for the synthesis of functional RNA such as transfer RNA or ribosomal RNA. However, these two types of RNA does not encode proteins, which is done by messenger RNA. For this, the transcription generates an RNA molecule that subsequently undergo translation in the ribosomes, the process by which a protein is generated. Many genes are composed of coding regions (exons) interrupted by noncoding regions (introns) that are removed during RNA processing. In prokaryotic cells is not the case for prokaryotic genes lack introns. The sequence of bases present in RNA determines the sequence of amino acids of the protein via the genetic code.
Other genes are not translated into protein, but perform their function as RNA. Among these genes are transfer RNA, ribosomal RNA, ribozymes and other small RNAs of diverse functions.
Some genes have undergone processes of mutation or other acts of reorganization and ceased to be functional, but persist in the genomes of living things. When to dispose function, called pseudogenes, and can be very similar to other genes in the body to be functional.
These amino acids include neutral groups, ie without charge, so they can form hydrogen bonds with water. A glycine is sometimes classified as nonpolar amino acid, because the group R is a simple hydrogen atom, too small to affect the polarity of the alpha amino groups and carboxyl alpha. In the amino serine, threonine and ceronina, the polarity is due to the presence of carboxyl group (-COOH) in the case of asparagine and glutamine.
Number of genes in some organisms Agency
Number of genes bp
Plants <50000 <10 11
Human 35,000 3 × 10 9
Mosca 12000 1.6 × 10 8
Hongo 6000 1.3 × 10 7
Bacteria 500-6000 5 × 10 5 - 10 7
Mycoplasma genitallium 500 580,000
Virus DNA 10-300 5000 to 800,000
Virus RNA 1-25 1000 to 23,000
Viroids 0-1 ~ 500
Prione 0 , 0
Changes in the genes
Diploid organisms (including almost all animals and plants) have two sets of homologous chromosomes, each from one parent. Each pair of chromosomes is thus a couple of copies of each gene, one from the mother and one father.
Some diseases like sickle cell disease (or sickle cell anemia) may be caused by a change in one gene (one of the 30,000 genes that constitute the plan for the entire human body).
Within a population of a species, genes may appear in different versions, with small variations in their sequence, and then are called alleles (one in Greek). Each of the alternatives that can take a gene within the population is an allele. Alleles may be dominant or recessive. When a single copy of the allele makes manifest the phenotypic trait, the allele is dominant. When requires two copies of the allele (one on each chromosome pair) to manifest its effect, the allele is recessive.
Regulation
A gene is the set of a particular sequence of nucleotides on one side of the "ladder" of chromosome referenced. The sequence may form proteins, or be inhibited, depending on the program assigned to the input cell chromosomes.
Environment of the genetic program
Every molecule tends to degrade its neutral charge state, being the time of expressing the load when the degradation is manifested in the loss of an electron or profit. In this interacting external and internal factors of the molecule with the medium. Since the case of two identical molecules with opposite charge, will tend to neutralize the charge by forming chemical bonds. These links can be ionic or covalent. The favorable trend is called 'Hook' (hook in English) and is the equivalent in our dimensions to the tendency of certain natural seeds to snag the hair of animals or even our socks.
The dynamics between the sample and the molecular dimension is parallel, in the following cases: There is no premeditation in the placement of the seed nor the place of the molecule in a given moment in time. It is not evident in nature a Ego intentional determined to finish it or not seeds if hooked in the hair of the animal, as there is no reason to think similarly in the case of two molecules, which coincide in space, have statistically likely to end almost certainly linked.
Under these premises, and c is true that the genetic program works. A completely autonomous process promoted by the dynamics of energy, through the inherent properties of each object which provides the physical description. Physical-chemical calculations provide a statistical approach to estimate in the most favorable results, determined by the least resistance when expressing their properties. This determinism is imponderable for physics calculations. In conclusion, the expression of the genetic program is well-known consequence of the butterfly effect.
Within what is the genetic program, we can say that is the memory of what happened in the species were adapted to an environment different from today, having reason to believe that past species were better adapted to the present and understanding the processes of extinction of the species are, therefore, another expression of natural selection.
The entropy associated with the tendency to disorganization of information makes this fact even more evident.
Fibrous and globular proteins are heteroproteínas consisting of layers.
Although known for more basic way of 3000 different protein molecules, have only been able to study in detail the structure of some portions that are essential in cell biology.