May 15, 1916—May 2, 1964


DAVID MAHLON BONNER’S short scientific career—he died at the age of 48—spanned the bloom period of Neurospora biochemical genetics and he was one of its main practitioners and contributors. He started life as a plant physiologist and became a biochemical geneticist working with Neurospora crassa after joining the group of George Beadle and Edward Tatum as a postdoctoral researcher at Stanford University. Initially he explored the use of Neurospora for biochemical investigations and identified intermediary steps in biochemical pathways. Finding that mutations that affect one enzyme are located on the same small segment of genetic material, he provided support for the “one gene, one enzyme” theory proposed by Beadle and Tatum in 1941. The nature of the genetic unit fascinated him: Was a genetic unit simple or complex? By analyzing 25 different mutants altered at the td (tryptophan desmolase) locus and a number of td revertants, he came to the conclusion that the genetic material controlling the formation of one enzyme represents a genetically indivisible unit, but admitted that (in 1955) it was still too early to decide whether this conclusion was fantasy or fact. His research group also found mutations that appeared to affect the rate at which an

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