Inside most of the cells in each human being resides molecules known as DNA, or deoxyribonucleic acid. These molecules are made up of four different bases which are assigned the letters G, C, A and T (for guanine, cytosine, adenine and thymine) and the manner by which these bases are arranged or sequenced defines the particular kind of protein that they will give rise to.
Given that humans are highly complex organisms, it is natural and correct to assume that we are made up of a huge number of different proteins that are coded for by an equally large number of different DNA sequences known as genes (Krogh, 2003).
The totality of an organism’s genes is known as its genome and since each gene provides the instructions for making a specific protein, the genome can be thought of as a collection or library of instruction manuals for producing all the proteins necessary for an organism to function normally and survive (Krogh, 2003).
This collection though, is not one that is built up as the organism grows but rather, one that is inherited from the organism’s parents. Human beings have 46 sets of these instruction manuals called chromosomes.
Chromosomes come in pairs but during reproduction, only half of each pair is passed on by each parent to their offspring so that the offspring would likewise end up having a total of 46 chromosomes (Krogh, 2003). This goes on for each new generation of offspring produced and so if we try to trace things back we can imagine how we have, for example, inherited the gene for our particular hair color from either our mother or father, and how they in turn have likewise inherited theirs from either of their parents.
Going a long way back towards our ancestors’ generation, we can therefore imagine ourselves as having inherited inside us a library of ancient instruction manuals which tell our body how to produce proteins practically the same way that they have been produced in our ancestors.
Naturally though it would be expected that during the course of time, modifications may have been made in these instructions but the fact still remains that these basic instructions were passed on from one generation to the next so that the information it carries may serve succeeding generations.