Heritable factors, determining the heritable properties of organisms.

Genes correspond to certain regions of DNA molecules, which are containing the genetic information for proteins. For the production of proteins, the DNA regions in question are first transcribed into mRNA molecules. Subsequently mRNA-molecules are translated into protein molecules.

In the case of eukaryotes various parts of the genes (introns) are excised from the mRNA molecules; the remaining sequences are named exons. Sequences preceeding the individual genes (promotors) determine the time and tissue in a given organism, where the respective gene is used for the production of proteins.