Ira Herskowitz

Geneticist who advanced the understanding of the way cells differentiate and a pioneer in the effort to learn how genetic differences among people influence the effectiveness of drugs. Known for his ability to clarify the most complicated biological questions, Dr. Herskowitz, a professor at the University of California at San Francisco, focused his research on Saccharomyces cerevisiae, commonly known as baker's yeast. It is the simplest single-cell organism that operates in a manner similar to a human cell. Herskowitz was born in Brooklyn seven minutes before Joel. The boys were mirror-image identical twins. Ira was left-handed, and Joel right-handed. They even parted their hair on opposite sides. The family moved to New Orleans and then to Bloomington, Ind., where the boys developed a love for both basketball and science, Joel Herskowitz said. There, at Indiana University, they would visit the genetics laboratory of their father, himself a biology professor, and were fascinated by the fruit flies he experimented with and by the smell of the ether that was used to kill the flies. After graduating from high school in the family's next hometown, St. Louis, Ira Herskowitz went to the California Institute of Technology, where he studied math and science. His twin went to Princeton. In addition to his twin, Joel, of Natick, Mass., he is survived by his parents, Dr. Irwin H. Herskowitz, an emeritus professor of biology at Hunter College in New York, and Reida Postrel Herskowitz, both of Lake Worth, Fla.; another brother, Alan, of Palenville, N.Y.; and a sister, Mara Herskowitz of New York City.