putting the genome to work : The human genome is in hand. The set of instructions embodied in the ancient chemical deoxyribonucleic acid, at least 3.5 billion years in the making, has been made fully visible for the first time. The manual with the specifications for the human species comes in 24 tapes of DNA, one for every chromosome, each carrying one long, punctuation-free sentence in evolution's four-letter programming code. Although exploration of the genome has already begun, it will be decades before every detail is thoroughly known.