The size of the issue

The body of a human being contains approximately 10¹⁴cells. Each one, in order for the whole to function properly, needs an appropriate repertoire of biochemical functions. Every cell has a unique history as to where it came from and how it got to be what it is; the history of a liver cell is not the same as that of a hair root cell. However, they all start with exactly the same genetic information. Every specialised biochemical function a cell performs is encoded within the same set of genes in the nucleus of that cell. Hence, genetics is important because genes determine what cells can do, and what cells can do is what organs, tissues and bodies can do!

In each nucleus there are approximately 100 000 genes. Deoxyribonucleic acid (DNA), the substance of genes, is a code in very simple molecular language. The code consists of four “letters”, “A” “T” “G” and “C”. The words of this code are three letters (or bases) long, each set of three coding for one amino acid in the resulting protein product. However, there is rather a lot of DNA; each human nucleus contains about three thousand million “letters” occupying approximately two metres of DNA (physical length unmagnified). A visual reconstruction of the DNA can be developed if you imagine …