NEW YORK (AP) ¿ Shares of Affymetrix Inc. dropped sharply Thursday after the genetic analysis technology company posted disappointing third-quarter results and offered a soft revenue forecast for the fourth quarter.

Shares of the Santa Clara, Calif., company tumbled $1.66, or 18.7 percent, to $7.20 in afternoon trading. On Wednesday, Affymetrix reported a larger loss and less revenue than Wall Street expected, and it said it expects $82 million to $85 million in revenue in the current quarter.

Thomson Reuters says analysts had been forecasting $85.7 million on average, with estimates ranging from $80.9 million to $89.9 million.

Affymetrix said it expects to sell more of its Axiom Genotyping system this quarter, but sales of consumable products that are used with Axiom will be slow as customers start using them. On Oct. 14, Affymetrix said Kaiser Permanente and the University of California at San Francisco will buy some Axiom systems to conduct a genetic analysis project.

Axiom is designed to help researchers find genetic variations linked with complex diseases.

In a note to clients, analyst Ross Muken of Deutsche Bank said genotyping revenue was weak in the third quarter due to a slowdown in research, and Affymetrix's costs increased. Muken predicted larger losses in 2009 and 2010 for Affymetrix, and kept a "sell" rating on the stock.

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