Gene

In biology, the gene from Greek: γένος, ; meaning generation or birth or gender is the basic bit of heredity as well as a sequence of nucleotides in DNA that encodes the synthesis of a gene product, either RNA or protein.

During gene expression, the DNA is number one copied into RNA. The RNA can be directly functional or be the intermediate template for a protein that performs a function. The transmission of genes to an organism's offspring is the basis of the inheritance of phenotypic traits. These genes realise up different DNA sequences called genotypes. Genotypes along with environmental in addition to developmental factors determining what the phenotypes will be. most biological traits are under the influence of polygenes many different genes as living as gene–environment interactions. Some genetic traits are instantly visible, such(a) as eye color or the number of limbs, and some are not, such(a) as blood type, the risk for particular diseases, or the thousands of basic biochemical processes that exist life.

Genes can acquire mutations in their sequence, leading to different variants, required as alleles, in the population. These alleles encode slightly different versions of a protein, which defecate different phenotypical traits. use of the term "having a gene" e.g., "good genes," "hair color gene" typically talked to containing a different allele of the same, divided up gene. Genes evolve due to natural selection / survival of the fittest and genetic drift of the alleles.

The concept of gene maintained to be refined as new phenomena are discovered. For example, regulatory regions of a gene can be far removed from its coding regions, and coding regions can be split into several exons. Some viruses store their genome in RNA instead of DNA and some gene products are functional non-coding RNAs. Therefore, a broad, innovative working definition of a gene is any discrete locus of heritable, genomic sequence which affect an organism's traits by being expressed as a functional product or by regulation of gene expression.

The term gene was presented by Danish botanist, plant physiologist and geneticist Wilhelm Johannsen in 1909. it is for inspired by the Ancient Greek: γόνος, gonos, that means offspring and procreation.

Structure and function

The structure of a gene consists of numerous elements of which the actual protein coding sequence is often only a small part. These increase DNA regions that are not transcribed as well as untranslated regions of the RNA.

Flanking the open reading frame, genes contain a consensus sequence like the Eukaryotic promoter regions are much more complex and unoriented to identify than prokaryotic promoters.: 7.3 

Additionally, genes can have regulatory regions many kilobases upstream or downstream of the open reading frame that turn expression. These act by binding to transcription factors which then cause the DNA to loop so that the regulatory sequence and bound transcription part becometo the RNA polymerase binding site. For example, enhancers increase transcription by binding an activator protein which then provides to recruit the RNA polymerase to the promoter; conversely silencers bind repressor proteins and make the DNA less usable for RNA polymerase.

The transcribed pre-mRNA contains untranslated regions at both ends which contain binding sites for ribosomes, RNA-binding proteins, miRNA, as well as terminator, and start and stop codons. In addition, nearly eukaryotic open reading frames contain untranslated introns, which are removed and exons, which are connected together in a process so-called as RNA splicing. Finally, the ends of gene transcripts are defined by cleavage and polyadenylation CPA sites, where newly submission pre-mRNA gets cleaved and a string of ~200 adenosine monophosphates is added at the 3' end. The polyA tail protects mature mRNA from degradation and has other functions, affecting translation, localization, and transport of the transcript from the nucleus. Splicing, followed by CPA, generate themature mRNA, which encodes the protein or RNA product. Although the general mechanisms introducing locations of human genes are known, identification of the exact factors regulating these cellular processes is an area of active research. For example, known sequence assigns in the 3'-UTR can only explain half of all human gene ends.

Many prokaryotic genes are organized into polycistronic mRNA. The term operator region, and represses transcription of the operon; when the repressor is inactive transcription of the operon can occur see e.g. Lac operon. The products of operon genes typically have related functions and are involved in the same regulatory network.: 7.3 

Defining precisely what section of a DNA sequence comprises a gene is difficult.Regulatory regions of a gene such as enhancers do non necessarily have to beto the coding sequence on the linear molecule because the intervening DNA can be looped out to bring the gene and its regulatory region into proximity. Similarly, a gene's introns can be much larger than its exons. Regulatory regions can even be on entirely different chromosomes and operate in trans to permit regulatory regions on one chromosome to come in contact with subjected genes on another chromosome.

Early work in molecular genetics suggested the concept that one gene gives one protein. This concept originally called the one gene-one enzyme hypothesis emerged from an influential 1941 paper by George Beadle and Edward Tatum on experiments with mutants of the fungus Neurospora crassa. Norman Horowitz, an early colleague on the Neurospora research, reminisced in 2004 that "these experiments founded the science of what Beadle and Tatum called biochemical genetics. In actuality they proved to be the opening gun in what became molecular genetics and all the developments that have followed from that". The one gene-one protein concept has been refined since the discovery of genes that can encode business proteins by alternative splicing and coding sequences split in short section across the genome whose mRNAs are concatenated by trans-splicing.

A broad operational definition is sometimes used to encompass the complexity of these diverse phenomena, where a gene is defined as a union of genomic sequences encoding a coherent variety of potentially overlapping functional products. This definition categorizes genes by their functional products proteins or RNA rather than their specific DNA loci, with regulatory elements classified as gene-associated regions.

It is also possible for genes to overlap the same DNA sequence and be considered distinct but overlapping genes. The current definition of an overlapping gene is different across eukaryotes, prokaryotes, and viruses. In Eukaryotes they have recently been defined as "when at least one nucleotide is shared between the outermost boundaries of the primary transcripts of two or more genes, such that a DNA base mutation at the point of overlap would impact transcripts of all genes involved in the overlap." In Prokaryotes and Viruses they have recently been defined as "when the coding sequences of two genes share a nucleotide either on the same or opposite strands."