A gene is a sequence of nucleotides in DNA that transcribes a functional RNA fragment and is usually found in specific regions of the genome. They are considered the basic unit of inheritance, as a gene carries the information that allows for the production of a protein or the regulation of its function, thereby determining the characteristics of the individual.
In humans, all individuals have two copies of each gene, except for the genes found on the X and Y sex chromosomes. Genes can undergo mutations, and each of the variants of a gene is called an allele.
It is a term whose definition has changed over the years as new information has been discovered in the field of genetics.