There are tens of thousands of genes in the human genome: minuscule twists of DNA and RNA that combine to express all of the traits and characteristics that make each of us unique. Each gene is given a name and alphanumeric code, known as a symbol, which scientists use to coordinate research.

According to this view, ancient viruses, as with the ones today, could only make copies of themselves by succesfully infecting a host. So they become engines of innovation, using every possible dodge to get their genetic payload inside the host cell. In an early, RNA-protein world, there would not be enzymes to degrade DNA, so a virus encoded by DNA would have a big survival advantage. This suggests a scenario in which a clever parasite brings along DNA plus the means of copying DNA-- a different parasite at least for bacteria and archaea/eukaryotes-- and hijacks the cell's existing interpretation equipment. The symbiosis of virus plus RNA/protein cell eventually resulted in the modern arrangement of DNA, RNA and protein.

The question is pretty simple: in the not-too-distant future you and I will have had our entire genomes sequenced (except perhaps those of you in California) - so how much hard drive space will our genomes take up?

Andrew calculates that a genome will take up about two CDs worth of data, but that's only if it's stored in one possible format (a text file storing one copy of each and every DNA letter in your sequence). There are other ways you might want to keep your genome depending on what your purpose is.

The executive summary For those who don't want to read through the tedious details that follow, here's the take-home message: if you want to store the data in a raw format for later re-analysis, you're looking at between 2 and 30 terabytes (one terabyte = 1,000 gigabytes). A much more user-friendly format, though, would be as a file containing each and every DNA letter in your genome, which would take up around 1.5 gigabytes (small enough for three genomes to fit on a standard data