## How are genes expressed?

In order for the genetic information encoded in DNA molecules to manifest itself even at the level of the phenotype, it is necessary that the genes are expressed. The term "gene" was introduced by Wilhelm Johannsen in 1909, when he defined it as a unit of genetic information that determines a specific phenotypic trait. This definition, although fairly accurate, does not describe the properties of a gene at the molecular level. The acquisition of new knowledge is gradually changing the formal definition of a gene. In terms of the expression of genetic information, the central dogma of molecular biology has long been valid, according to which genetic information is usually copied from 1) DNA to DNA during intergenerational transmission and 2) from DNA to proteins during gene expression. To take the genetic information from DNA to proteins, the transfer requires two steps. The first step is transcription, where the information from DNA is transcribed into an RNA molecule. From this, the information is subsequently translated into the sequence of amino acids forming the polypeptide chain. Such a process is called translation and leads to the formation of proteins (Figure 3.6).