gene

A gene is the basic unit of heredity, much like a single entry in a vast instruction manual carried inside every cell. Where a recipe book tells a kitchen how to make each dish, the genes tell a cell how to build and run a living body, one instruction at a time.

Physically, a gene is a stretch of DNA at a specific place on a chromosome. Most genes encode the information needed to make a protein; the cell reads the gene, copies it into a messenger molecule, and uses that copy as a template to assemble the protein. Proteins then do the real work of the body, acting as enzymes, structural parts, and signals.

Because a gene can come in several alternative versions, called alleles, different individuals can carry different forms of the same instruction. This is the molecular root of inherited differences: the same gene, read in slightly different spellings, can give brown or blue eyes, or a working or faulty enzyme.

The tidy phrase “one gene, one trait” is a useful starting point but often misleading. Many genes contribute to a single trait, one gene can influence several traits, and not every gene makes a protein at all. The modern definition treats a gene as a unit of DNA that produces a functional product, whether a protein or a working RNA molecule.