Cytological Analysis of X-Ray-Induced Mutations at Eight Specific Loci in the Third Chromosome of Drosophila Melanogaster.

The application of cytogenetic techniques to studies of radiation effects gives a measure of the physical damage to the chromosomes. Such qualitative and quantitative measures of the chromosomal damage and correlation of these results with genetic tests are necessary for the detection and separation of mutational pattern differences in various types of germ cells or mutational pattern differences as a result of various types of radiation. It is with this combination of cytological and genetic techniques that we come closest to determining the exact nature and extent of heritable damage to the organism. Numerous investigations on the induction of lethal and visible mutations have been carried out; however, in many instances, cytological analysis of these mutations to determine the chromosomal changes associated with the genetic changes has not been practical. Much of the material was not suitable for a detailed cytological analysis, but with the discovery that the salivary gland chromosomes of the dipterous insects could be used for cytogenetic analysis (PAINTER 1933), Drosophila melanogaster became the ideal organism for such studies. The first application of combined genetic and cytological tests to a group of X-rayinduced specific autosomal mutations was by PAINTER and PATTERSON (1935) who used X-ray-induced mutations a t eight specific loci in the autosomal third chromosome of D. melanogaster. (See also ALEXANDER 1954.) The present investigation also combines genetic and cytological analyses. The X-ray-induced genetic damage was recovered as visible mutations at eight specific loci on the third chromosome of D. melanogaster, seven of which were used by PAINTER and PATTERSON. These mutants were analyzed genetically for viability and cytologically for the presence of chromosomal aberrations. In addition to the determination of the types and frequencies of the chromosomal changes, the types and frequencies of changes induced in the ma-