Abstract
The action of radiant energy in inducing gene mutations and various types of chromosomal alterations has been known for several years. 1 , 2 The alterations produced have involved changes in parts of chromosomes, whole chromosomes and apparently in the composition of individual genes. In Muller's classic report 1 on the artificial production by X-rays of alterations in the hereditary material of Drosophila melanogaster, evidence was presented, through breeding experiments, of the occurrence of dominant lethals. These are lethals whose presence in single dose can cause the death at various stages of development of the zygotes which contain them and thus are never transmitted to succeeding generations. Such dominant lethal genetic changes may be induced by X-rays in germ cells and then contributed to the zygote by one of the gametic nuclei. As yet, however, little is known of how the inviable nuclear alterations act to modify development. It is the purpose of this report to deal with certain aspects of this question.
The random effects of the radiations on the chromosomes of Drosophila have been reported elsewhere. 3 It was observed that the meiotic and mitotic divisions can become drastically disordered following treatment of the germ cells with X-rays. The achromatic figures as well as the chromosomes proper are frequently aberrant. In the zygotic mitoses chromosome fragmentation and elimination, asymmetrical divisions, multipolar divisions of the tri-polar and quadripolar types and pycnotic, clumped chromosomal complexes with occasional chromatic bridges were noted and described. These induced abnormalities were considered to be directly responsible for the greatly increased percentage of mortality among the offspring, since the frequency of organisms showing such mitotic abnormalities was found to be about equal to the frequency of zygotic lethals.
Get full access to this article
View all access options for this article.