How Do They Do It?
In February of 2001 it was announced that the human genome had been sequenced by two research groups. The publicly funded Human Genome Project and Celera Genomics. There were two processes used by these researchers. The original method is called the BAC to BAC (clone-by-clone) method. The newer method is called whole genome shotgun sequencing.
To start the sequencing, the genome is broken up into small pieces. The A,C,G,T base pairs are sequenced and then the genome is put back together.
Sequencing the genome will help scientists understand it and make it easier to find specific genes, and to perhaps help them understand how the genes work together to make a human operate. There is also that part of the DNA called junk DNA and it is called this simply because we don't know what it does or if it does anything at all.
The first approach, the BAC to BAC approach requires breaking the genome into large chunks of about 150,000 base pairs, mapping the genome so that they know where on the genome each chunk belongs, and then cutting the chunks smaller still, about 500 base pairs long. When they have sequenced these smaller pieces they put them back together. The second method, the whole genome shotgun method simply cuts the genome up into small pieces in the beginning bypassing the mapping. Then they perform the sequencing, and put the genome back together. There are advantages and disadvantages to both methods of sequencing. the BAC to BAC method is accurate but the mapping process is extremely tedious and slow. The shotgun method is potentially very fast but putting all those tiny pieces back in the right place can be extremely difficult.
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