It can be represented as a series of letters, turning chemicals into text. As such, it can be read directly. This is true, but even leaving aside the problem of interpretation (what these letters in a particular order mean), there is another fundamental issue that genome researchers must address first: the sheer quantity of the data they are dealing with.
So far, the digital content of the genome has been discussed in the abstract. To understand why computers are indispensable, though, it is helpful to consider some specific facts. For example, the DNA within a typical human cell is twisted into a double helix; this helix is wound up again into an even more convoluted structure called a chromosome. Chromosomes were first noted within the nucleus of certain cells over one hundred years ago, but decades were to pass before it was shown that they contained DNA. Normal human cells have 46 chromosomes—22 similar pairs, called autosomes, and the two sex chromosomes. Women have two X chromosomes, while men possess one X chromosome and one Y chromosome. The number is not significant; chromosomes are simply a form of packaging, the biological equivalent of CD-ROMs.
Even though these 46 chromosomes (23 from each parent) fit within the nucleus, which itself is only a small fraction of the microscopic cell’s total volume, the amount of DNA they contain collectively is astonishing. If the DNA content of the 23 chromosomes from just one cell were unwound, it would measure around 1 meter in length, or 2 meters for all 46 chromosomes. Since there are approximately one hundred thousand billion cells in the human body, this means that laid end-to-end, all the DNA in a single person would stretch from the earth to the sun 1,200 times.
Things are just as dramatic when viewed from an informational rather than physical point of view. Each of the two sets of 23 chromosomes—found in practically every human cell—makes up a genome that contains some 3 billion chemical digits (the As, Cs, Gs and Ts). Printed as ordinary letters in an average-sized typeface, a bare listing representing these letters would require roughly 3,000 books each of 330 pages—a pile about 60 meters high. And for any pair of human beings (except twins deriving from the same fertilized egg), every one of the million pages in these books would have several letters that are different, which is why some people have brown eyes and others blue.
What is the truce (hudna) that Hamas offers?
