Biomedical Engineering Reference
In-Depth Information
DNA is made up of an alphabet of four letters, rather than the 26 we use
in English. These DNA letters are called 'base pairs'. The human genome
is about 3 billion DNA base pairs in length. This makes the maths of
working out the cost of sequencing each base pair a remarkably simple
affair of dividing the total $3 billion project cost by 3 billion, giving us a
dollar per base pair. Given that each base pair can be coded by 2 bits of
information then the whole genome could be stored on about 750 MB of
disk space. The cost of storing this much information, even 10 years ago
would only be a few dollars, making the data storage costs a microscopic
percentage of the overall project costs.
22.2.2 Things get a little more complex
There were huge celebrations in the scientifi c community when the
human genome was published, but this was really only the beginning of
the work that needed to be done to get value from the genome. The next
step was to read and understand the information in the 46 volumes.
Fortunately, just like in an encyclopaedia the genome is broken down
into a number of entries or articles. In the world of genetics these entries
are called genes. As humans are quite complicated animals, it was
expected that we would have a large number of genes, many more than
simpler organisms such as worms, fl ies, plants, etc. All we had to do was
work out which gene corresponded to a given human trait and we would
have unlocked the secrets to human biology, with hopefully fantastic
benefi ts to healthcare. Unfortunately, there was a problem, it turned out
that there were far fewer genes in humans than originally expected. The
total number of genes in the human genome was found to be around
23 000. To put this in perspective that is about 9000 genes less than the
corn that grows in our fi elds has, and only just 7000 more than a very
simple worm.
As scientists investigated further, new levels of complexity were
discovered. If we keep with the analogy of the genome as an encyclopaedia,
genes can be thought of as the topics within it. Researchers discovered
that paragraphs within each topic could be read or ignored, depending
on circumstances, which would change the meaning of the article (this is
known as splice variants in genetics). They also found many spelling
changes, small additions or omissions from one person's genome to the
next. It soon became apparent that these differences were the key to
unlocking many more secrets of the human genome. Initially it was only
possible to investigate these differences on a very small scale and on very
Search WWH ::
Custom Search