Gene (biology)

A gene (also called a hereditary unit) is a segment of DNA (the nucleic acid that stores information in cells) containing instructions for building a protein or producing a functional RNA. Genes are the basic units of heredity (inheritance), and they are the means by which traits pass from parents to offspring.

Genes are located on chromosomes, which are long structures made up of DNA and proteins bound together. Each species has a characteristic number of chromosomes and genes. Mutations in the DNA of a gene can alter how the protein it codes for functions, and this can affect the health or appearance of organisms.

Structure

DNA consists of two intertwined strands, each containing four types of bases: adenine (A), thymine (T), guanine (G), and cytosine (C). The sequence of these bases carries the gene's information. A typical gene contains a region that is transcribed into protein (known as an exon in some organisms) and a region that is not transcribed, as well as regulatory elements (a promoter) that determine when and how often the gene is active.

How genes work

Gene function proceeds in two major steps. First, the DNA is copied into an RNA molecule (transcription). Next, the RNA message travels to the ribosome, where three-base sequences (codons) are translated into amino acids that link together to form a protein (translation). This protein carries out the cell's functions: enzymes, the structure of the cell, and signaling throughout the body.

Inheritance

Many organisms, including humans, inherit two copies of each gene—one from the mother and one from the father. These different versions are called alleles. Some alleles are dominant, while others are recessive, which determines how a particular trait appears. Gregor Mendel, a scientist in the 19th century, conducted careful experiments establishing the laws of inheritance before the structure of DNA was known.

Research and applications

Modern technologies have made it possible to read the sequence of DNA (sequencing), to alter or repair genes, and to identify diseases caused by hereditary factors. Applications include personalized medicine, agriculture, and the study of evolutionary history.