MCCLINTOCK 199 



lowing expression of its attitude Japanese material. In contrast to labo- 

 toward the genetic program: "Al- ratory data, this material is too much 

 though there is every reason to infer influenced by extraneous variables and 

 that genetic effects can be produced too little adapted to disclosing genetic 

 and have been produced in man by effects. In spite of these facts, the con- 

 atomic radiation, nevertheless the con- ference feels that this unique possibil- 

 ference wishes to make it clear that it ity for demonstrating genetic effects 

 cannot guarantee significant results caused by atomic radiation should not 

 from this or any other study on the be lost." 



The Origin and Behavior of Mutable Loci in Maize 



BARBARA MCCLINTOCK 



Reprinted by author's and publisher's permis- 

 sion from Proceedings of the National Academy 

 of Sciences, vol. 36, 1950, pp. 344-355. 



A point that has been neglected m the introductions to these 

 papers has been the give a?id take that exists between the two 

 branches of biology, which is implicit in the study of genetics. Me?2- 

 dePs original work was based 07i a pla?it species. Cuenot discovered 

 that Mendel's laws applied equally well and were readily observable 

 in the mouse. Since this beginning the botanists and zoologists have 

 had to keep a close eye on each other, with discoveries of genetic 

 pheyjomena in one kingdom rapidly extrapolated into the other. It 

 has long been obvious that the differences between plajits afid ani- 

 mals were, not extrejfiely significa?it on the level of the gene, a7id that 

 genetics is properly a scietice of biology, reqiaring a knowledge of 

 both botany and zoology. 



McClintock''s paper deals with a phenome?wn thoroughly studied 

 in Drosophila, which she found occurrifig i?i cor?i. The value of this 

 paper lies in the fact that she was obviously not satisfied solely with 

 the discovery of a comynon phenomenon between plant and animal, 

 but then worked out the way in which the evejjts took place. The 

 existence of a?i ^''activatof gene, which expresses itself primarily by 

 influencifig the mutation of a second gejie, was new and interesti?ig. 

 This paper establishes the jnutagenic effect of one jnember of the 

 gene co?nplex upo?i another, and provides an internal as well as the 

 more widely demonstrated and fajniliar external source of mutation. 



