to take a collection of Neurospora cultures with him from Columbia to the 

 new Biology Division of the Cahfornia Institute of Technology, which he 

 established in 1928. 



Shortly thereafter when Carl C. Lindegren came to Morgan's laboratory to 

 become a graduate student, it was suggested that he should work on the genetics 

 of Neurospora as a basis for his thesis. This was a fortunate choice, for Linde- 

 gren had an abundance of imagination, enthusiasm and energy and at the 

 same time had the advice of E. G. Anderson, C. B. Bridges, S. Emerson, 

 A. H. Sturtevant and others at the Institute who at that time were actively 

 interested in problems of crossing over as a part of the mechanism of meiosis. 

 In this favorable setting, Lindegren soon worked out much of the basic 

 genetics of Neurospora. New characters were found and a good start was 

 made toward mapping the chromosomes. 



Thus, Tatum and I realized that Neurospora was genetically an almost 

 ideal organism for use in our new approach. 



There was one important unanswered question. We did not know the mold's 

 nutritional requirements. But we had the monograph of Dr. Nils Fries, which 

 told us that the nutritional requirements of a number of related filamentous 

 fungi were simple. Thus encouraged, we obtained strains of Neurospora crassa 

 from Lindegren and from Dodge. Tatum soon discovered that the only 

 growth factor required, other than the usual inorganic salts and sugar, was 

 the recently discovered vitamin, biotin. We could not have used Neurospora 

 for our purposes as much as a year earlier, for biotin would not then have been 

 available in the quantities we required. 



It remained only to irradiate asexual spores, cross them with a strain of 

 the opposite mating type, allow sexual spores to be produced, isolate them, 

 grow them on a suitably supplemented medium and test them on the un- 

 supplemented medium. We believed so thoroughly that the gene-enzyme- 

 reaction relation was a general one that there was no doubt in our minds that 

 we would find the mutants we wanted. The only worry we had was that their 

 frequency might be so low that we would get discouraged and give up before 

 finding one. 



We were so concerned about the possible discouragement of a long series 

 of negative results that we prepared more than thousand single spore cultures 

 on supplemented medium before we tested them. The 299th spore isolated 

 gave a mutant strain requiring vitamin B6 and the i 085th one required Bi. 

 We made a vow to keep going until we had 10 mutants. We soon had dozens. 



Because of the ease of recovery of all the products of a single meiotic process 



s-35 



