A gene is a segment of DNA that codifies proteins required in the development and biological activity of any living being. Some genes direct the synthesis of one or more proteins; while some others have a regulatory role (they control other genes» activities). Proteins are specific for each species, and every single protein plays a particular role within an organism.

They can be enzymes catalysing biochemical reactions, hormones, immunoglobulin or oxygen or other compounds transporters (as haemoglobin), as well as they can carry out some other biologically vital functions. These functions are not only determined by their chemical composition but also by the way they are folded which is the key to their mission. For instance, the mad-cow disease prion was a misfolded protein.

Superior organisms keep their DNA locked in their cell nucleus, composing large rolled up chains within their chromosomes. Every cell of an organism holds the same genetic resources, although they play very different roles depending on which genes are activated in each of them: some cells are specialized in absorbing solar energy and transforming it into chemical energy, whereas some others see that water and nutrients are absorbed; this way, there are some cells that collaborate on the plant's growing, some other cells have a reproductive role… Every one of those cells is always synthesising only those elements they need. For this ends, they have complex mechanisms of gene regulation, where other genes and cell compounds take part, so that only one protein is produced where and when needed.

The theory the genetic engineering was based on at the beginning –where every gene codifies one single protein- crumbled down when the human genetic code was deciphered in 2001 proving that the number of genes of a human being does not differ so much from a worm's. How is it possible? It has been proven that each gene can produce several proteins depending on the instructions received. The genetic information is often edited during the process of protein synthesis, generating several different compounds.

On the other hand, even though the way the process of gene regulation is conducted is not accurately known, it is becoming more obvious that genes do not act individually but they work in team, interacting upon each other and upon other genetic and cell elements. They are extremely sophisticated process able to fulfil the organism needs and to react to the stimulus of an environment which is continuously changing.

According to recent researches: “A genome, the sum of heritable information that is held in the chromosomes and that governs how an organism develops, is not a static text passed from one generation to the next. Rather a genome is a biochemical machine of awesome complexity.” W. Wayt Gibbs1

WE DON'T HAVE MORE GENES THAN A WORM
It turned out that persons have many less genes than it was thought until the human genetic code was deciphered –grosso modo- in 2001.