Illumina makes machines that use blood or tissue samples to decode a person's entire genetic makeup in about a week--a process known as DNA sequencing. Top government and academic research centers are the machines' main buyers now, but the technology's supporters have said it will eventually trickle down through the health-care system, helping doctors prevent and treat illness. Roche had launched a tender offer of $44.50 a share for Illumina, valuing the company at about $5.7 billion. A U.S. spokeswoman for Roche said the company considers its bid a full and fair offer and is still reviewing the latest response from Illumina. Illumina called the Roche offer opportunistic and said it valued the company below recent trading levels. The genetic-technology company also said the takeover offer introduced significant uncertainty and risk.