What is a gene?

What a gene is

A gene is a defined sequence of DNA — a string of the bases A, T, G, and C — that carries the code for a functional product. Most genes encode proteins, but many encode functional RNA molecules such as transfer RNA or ribosomal RNA. A gene typically includes the coding sequence together with regulatory regions, such as a promoter, that control when and how strongly it is expressed. In organisms with complex cells, coding regions (exons) are often interrupted by non-coding stretches (introns) that are removed when the gene is processed.

Loci, alleles and inheritance

Each gene sits at a particular position, or locus, on a chromosome. Because most plants and animals carry two copies of each chromosome, they carry two copies of most genes — one from each parent.

Alternative forms of a gene are called alleles. The combination of alleles an organism carries (its genotype) interacts with the environment to produce observable traits (its phenotype). Patterns of dominant and recessive alleles, first studied systematically by Gregor Mendel, explain much of how traits are inherited.

From gene to function

A gene exerts its effect through gene expression: its DNA sequence is transcribed into RNA, and protein-coding genes are then translated into proteins. The protein products carry out structural, enzymatic, signalling, and regulatory roles in the cell. Whether and how strongly a gene is expressed is tightly regulated, so the same set of genes can produce very different cell types within one organism.

Genes in research and standards

Cataloguing genes, naming them consistently, and linking them to functions is a major task of genomics and bioinformatics. Organisations such as the HUGO Gene Nomenclature Committee maintain approved gene names and symbols so that researchers worldwide refer to the same gene unambiguously — a form of controlled vocabulary that supports findable, interoperable, and reusable data.