measures them, roundish viruses range from around fifteen nanometers (that’s fifteen billionths of a meter) in diameter to around three hundred nanometers. But viruses aren’t all roundish. Some are cylindrical, some are stringy, some look like bad futuristic buildings or lunar landing modules. Whatever the shape, the interior volume is minuscule. The genomes packed within such small containers are correspondingly limited, ranging from 2,000 nucleotides up to about 1.2 million. The genome of a mouse, by con