How was it done?
Your gene instructions are grouped into two sets of 23 'volumes', known as chromosomes, each containing millions of DNA letters, or base pairs. To help them read the entire human genome, scientists took each ‘volume’ and compiled an 'index' – a chromosome map. Some of the landmarks on these maps are genes, others are just short sections of non-coding DNA.
How was the DNA sequence read?
To read the order of letters – or base pairs – in the DNA code, scientists must first break up each chromosome into a set of overlapping pieces. They then use machines to read the order of the letters (the DNA sequence) in each piece. With the aid of computers and the chromosome maps, they reconstruct the order of letters in the complete chromosome.