ADDITIONAL EVIDENCE ON THE EFFECT OF X-RAY AND ULTRAVIOLET RADIATION ON MUTATION IN MAIZE

Abstract

With the advent of superior cytological techniques such as PAINTER’S salivary gland method in Drosophila and MCCLINTOCK’S pachytene technique in maize and their use in the analysis of the various X-ray induced cases, it became quite clear that the majority of the X-ray induced alterations were actually chromosomal alterations or extragenic changes. Taking a skeptical approach, STADLER began a rather extensive study of individual X-ray induced changes at particular loci in maize to determine whether or not they were actually discrete changes of the gene itself. Such criteria as association with a visible chromosomal aberration, transmission through male and female germ cells, viability of the homozygote, and ability to revert to the original nonmutant form were used in this determination. STADLER (1954) could find no evidence that X-rays cause gene mutation. He suggested that in view of the data a re-examination of our definition of the gene might be necessary. As the number of radiation experiments multiplied, two important aspects of the problem arose. The first was the discovery of a type of position effect in Drosophila in which an X-ray induced chromosomal aberration that removed a locus, normally residing in euchromatin, to a new position next to heterochromatin could cause that locus to express itself as a mutable allele. The new form generally showed a mosaic of dominant and recessive phenotypes. If this locus was moved away from the heterochromatin it reverted to the normal wild type allele. This behavior satisfied Journal Series Paper No. 1675 approved by the Director of the Missouri Agricultural ExperiThis work was supported in its initial stages by a grant from the Atomic Energy Commission. ment Station.