Genes determine a person's inherited traits. They contain the building blocks for proteins that guide the person's individual development. In practice, one gene directs the production of one protein.

Tens of thousands of different proteins, such as hormones, enzymes, antibodies or other vital building blocks, are formed in the human body according to the instructions stored in the individual's genes. For the human body to function, the production and function of all these different proteins must be in order.

The function of genes is complex and still needs to be explored. It has been found that although every human cell contains all human genes, the active and functional genes in each cell are specific to that cell type. For example, a muscle cell contains genes that control hair growth, but these genes do not work. Similarly, all cells have genes that guide the early development of an embryo, but they do not function after the embryo has developed into a fetus and an adult.

Determining hereditary traits can be complicated, because their expressions are influenced by many hormones and other factors. For example, baldness is a dominant feature caused by a protein produced by alleles. However, this allele that affects baldness only works in the "right environment," that is, when an individual has enough testosterone in their body. For this reason, a woman can carry the baldness allele, but will not become bald because of it.