Scientists know that different types of cell switch on different collections of genes. How they get to this point, however, is still an area of intense research. The behaviour of each gene is governed by associated regions of DNA. This influences the ability of proteins called transcription factors - which can switch genes on or off - to read that gene. So how do these regions of DNA manage to perform this feat? The answer is epigenetics.

The genome can be compared to a musical score. The notes in the score represent the DNA sequence of a gene. Epigenetics comes in to play through dynamics and phrasing - telling a cell how genes are to be played: forte (loud), pianissimo (really softly), etc. The dynamics and phrasing of the genome are the work of proteins that package our DNA into chromosomes.