Spontaneous chromosome change

X-Ray fractionation and chromosome breakage

“…For example, the configuration illustrated in plate II, fig. 5, a dicentric ring at anaphase, could result from an earlier centric ring or a centric fragment with sister reunion at both ends (see Darlington and Upcott, 1941). Similarly, the odd dicentric in plate II, fig.…”

“…The method of scoring is based on that elaborated by Darlington and Upcott (1941) and Darlington and La Cour (i94). This method enables the various events occurring from the time of irradiation to observation of the resulting chromosome configurations to be 8 G. R. LANE separated, as far as possible, and is considered to be the most complete and consistent in observation and inference.…”

“…14). These configurations are considered to be due to delayed restitution of one of the chromatids with or without reunion of the other, in both cases following chromosome breaks (see Darlington and Upcott, 1941 ;La Cour, 1945, andKoller, 1947). The occasional occurrence of a slight constriction in the unbroken chromatid, at the same locus as the break in the sister chromatid, confirms this interpretation ( fig.…”

Asynapsis and spontaneous chromosome breakage in scilla

“…Of 22 cells with bridges counted out of 825 pollen mother cells at first anaphase in one plant, 5 cells show single bridges without fragments. In these cases the bridges may well be the result of failure of division of end genes (sister reunion), brought about by nucleic acid upset, as suggested by Darlington and Upcott (1940) in explanation of similar bridges seen in Tradescantia (Darlington, 1937), and in Pisum (Koller,I 938), and also at mitosis in Trillium (Darlington and La Cour, 1945).…”

“…Such breakage in pollen mother cells would seem to be of rare incidence. A case mentioned in Tulipa orphanidea (Darlington and Upcott, 1940) was beyond analysis. Breakage may or may not have been associated with reduced chiasma frequency and consequent asynapsis.…”