[ Gene ]
A region of DNA in which the structural sequence encodes a biological trait or characteristic.
Genes are replicated by cell division and modified by recombination in sexual reproduction and by mutation. They are the basis of inherited traits by biological offspring.
Biochemically, a gene is a sequence of nucleotides, the building blocks of DNA, the order which determines what it expresses.
Gene expression are activated or “switched on” by external factors such as environment. This is studied in the field of epigenetics, a branch of the field of genetics.