Irradiation of condensed meiotic chromosomes in lilium longiflorum

Linear dose-response of acentric chromosome fragments down to 1 R of x-rays in grasshopper neuroblasts, a potential mutagen-test system

Grasshopper-embryo neuroblasts have no spontaneous chromosome breakage; therefore they permit easy detection of agents that break chromosomes. An X-ray exposure of 1 R induces in them a detectable number of chromosome fragments. The dose-response of acentric fragment frequency fits a linear model between 0 and 128 R. Thus another cell type is added to those previously demonstrated to have no threshold dose for the induction of chromosome or gene mutations.

Half-chromatid aberrations and chromosome strandedness

If cells are irradiated during prophase, at anaphase they may show a side-arm bridge type of configuration. These have usually been interpreted as half-chromatid aberrations and they have been used as evidence that chromosomes are multistranded. It is the purpose of this paper to emphasize that such a configuration may just as easily arise on the basis of a single-stranded chromosome, and that the data on the type of aberrations found at the next mitosis (M2) suggest that chromosomes are single-stranded.