The classical X-ray work. I: Mutations. The target theory

Abstract

Soon after the discovery of X-rays by Röntgen at the turn of the century, the effects of this new powerful type of radiation on biological systems were studied. Embryological and cytological disturbances were observed in a variety of organisms, and this led to attempts at influencing heredity by radiation. Indications that X-rays may produce hereditary changes in germ cells were obtained quite early, but decisive proof had to wait for the development of systems in which nuclear mutations could be clearly distinguished from other types of damage to e. g., the spindle apparatus or the cytoplasm, and in which mutation frequencies could be objectively measured. In the 1920s such systems became available in Drosophila and maize. The first definite proof for the mutagenic action of X-rays was obtained in 1927 by Muller on Dosophila (1)to be followed a year later by Stadler’s evidence for the production of mutations in maize (2). Even before this, Drosophila techniques had made it possible to discover X-ray effects on non-disjunction (3) and crossing-over (4,5). Since most of the classical X-ray work was done on Drosophila, this is the place to describe the two main tests used at that time and still used widely; the test for sex-linked lethals and the test for sexlinked visibles.