Showing papers on "Sister chromatid exchange published in 1970"

The analysis of exchanges in Tritium-labelled meiotic chromosomes. 1.

Abstract: The autoradiographic analysis of exchanges in tritium-labelled meiotic chromosomes is potentially a useful approach to the study of meiotic exchange events since this method differentially labels meiotic chromatids along their entire length. The main problem encountered in earlier autoradiographic studies is that of distinguishing label exchanges generated at chiasmata from label exchanges generated by sister chromatid exchange. This problem was overcome in the present study by the choice of a meiotic system (male meiosis of Stethophyma grossum) where chiasmata are limited to just one proximally localised chiasma in each bivalent. This system allows the positive identification of chiasma-generated label exchanges and demonstrates convincingly the origin of chiasmata through breakage and rejoining of homologous non-sister chromatids. Sister chromatid exchanges are also readily detected in labelled meiotic chromosomes of this species, where they occur with a mean frequency of 0.35 per chromosome. This frequency is similar to that found in mitotic spermatogonial cells and the exchanges are randomly distributed both within and between chromosomes. These features of meiotic sister chromatid exchanges suggest that they are unrelated to non-sister chiasmatic exchanges and they probably have no special meiotic significance.

Induction of chromosome aberrations by X-rays and chemical mutagens in a desynaptic mutant and in wild-type barley

Abstract: It has previously been proposed that eukaryotes with a genetically determined abnormality in the sequence of events leading to normal chromosome exchange at meiosis, might be expected to show an altered response on the part of their somatic cell chromosomes following exposure to chemical or physical mutagens. As part of a programme undertaken to examine this contention, dry and soaked seeds of a wildtype (Ds Ds) and a desynaptic mutant (ds ds) of barley were exposed to X-rays and the frequency of chromosome-type aberrations determined in cells in their first post-irradiation mitosis. Preliminary experiments with these materials by Riley and Miller had pointed to an increase in yield of aberrations in cells of the mutant relative to the normal, but no such difference could be demonstrated in the present more extensive experiments. Seeds and root-tips were also exposed to the chemical mutagens nitrogen mustard and diepoxybutane and a detailed analysis of the induced chromatid-type aberrations revealed no difference in the sensitivity of ds ds and Ds Ds genotypes. The frequency of sister chromatid exchange were studied in autoradiographs of root-tip cells in their second mitosis following exposure to [3H]thymidine. There was no difference in the incidence of such exchanges between cells from the different genotypes.