J. R. S. Fincham was distinguished for his pioneering contributions to biochemical genetics and microbial genetics. In the 1940s and early 1950s, George Beadle, Edward Tatum and Joshua Lederberg launched the new field of microbial genetics (for which they were awarded the Nobel Prize in 1958). It was discovered that single gene mutations blocked single metabolic steps and this led to the 'one gene-one enzyme' hypothesis. This powerful prediction was not supported by experiment for some years, and it was John Fincham who first obtained direct evidence that it was correct, using am mutants in the fungus Neurospora crassa that were deficient in a specific enzyme (glutamate dehydrogenase). He exploited these mutants and the gene product in many biochemical and genetic studies for much of the rest of his career.
John Robert Stanley Fincham was born in 1926, the son of a nurseryman father and schoolteacher mother, and educated at Hertford Grammar School and Peterhouse, Cambridge, where he read Natural Sciences. After his first degree he studied for a PhD under the supervision of D.G. Catcheside in the Botany School, Cambridge, a laboratory that produced several influential geneticists. During his postgraduate research he worked for one year at the California Institute of Technology with Sterling Emerson, in a laboratory that was the stronghold of Neurospora genetics. In 1950, the year he married Emerson's daughter Ann, he became a Lecturer and, from 1954, Reader at University College, Leicester (granted its Royal Charter as Leicester University in 1957), moving in 1960 to head the Genetics Department of the John Innes Institute. He went to Leeds University in 1966, as the first Professor of Genetics. Ten years later he was appointed to the Buchanan Chair of Genetics at Edinburgh University, and then, in 1984, to the Balfour Chair of Genetics at Cambridge University " he was the only geneticist to have held both these prestigious professorships.
He was elected a Fellow of the Royal Society in 1969, and a Fellow of the Royal Society of Edinburgh in 1978. He was awarded the Emil Christian Hansen Medal in 1977. He retired in 1991, returned to Edinburgh and remained active in teaching and research.
In the late 1950s, an unexpected discovery was made in several laboratories. This was that the fact that some mutations in the very same gene complemented each other to produce enzyme activity, whereas it was previously thought that only mutations in different genes should complement each other. Fincham exploited his am mutant system to demonstrate for the first time that this complementation was due to the formation of enzymes with at least two protein sub- units (in his case six sub-units), where different mutations in separate sub-units corrected each others' deficiency to produce enzyme activity. Fincham reviewed all this work, and much else, in his book Genetic Complementation (1966). …