Gene as the Functional Unit of Inheritance

A gene is the basic physical and functional unit of heredity. Gregor Mendel worked out the rules by which traits pass from parents to offspring in the 1860s, but he never used the word 'gene' -- he called his hereditary units 'factors'. The term 'gene' itself was coined only in 1909, by the Danish botanist Wilhelm Johannsen, to name the discrete determiners of inherited characters that Mendel's factors implied. In 1902 Walter Sutton put forward what is called the classical concept of the gene: genes are discrete particles that obey Mendel's rules of inheritance, sit at a fixed, definite position (locus) on a chromosome, and are individually responsible for producing one specific observable trait. From this classical concept flow several defining properties. A single organism carries many more genes than it has chromosomes, so several genes must be strung along any one chromosome; those genes are arranged in a fixed, linear order, like beads threaded on a string, and each one occupies its own specific locus. A gene can exist in the population as several alternative forms, called alleles, differing slightly in sequence but occupying the same locus. Genes can also undergo sudden, heritable changes in their posi …