A genically determined abnormality in the number and arrangement of basal bodies in a ciliate

Abstract

When an F 1 of a cross between clones K 7 and VF 17 of Euplotes minuta was backcrossed to the K 7 parent, 6 of the 30 progeny clones displayed a syndrome of abnormalities in cortical pattern, which included (1) substantial reduction in number of dorsal cilia, (2) a lesser reduction in number of ciliary rows, (3) absence of one or both right caudal cirri, (4) appearance of incomplete and abnormally oriented membranelle bases, (5) irregularities in form of ventral cirri. The length of cilia and arrangement of subpellicular fiber bundles were fully normal in these 6 clones, as were cell size and division rate. A test cross of one of these abnormal clones with the F 1 parent yielded a 1:1 segregation of normal and abnormal progeny clones, with no intermediate clones, suggesting a single-gene basis for the abnormal condition. Comparison of development in normal and abnormal clones suggested that the abnormal clones were defective in the formation of basal bodies; new basal bodies often failed to form at the expected sites, and occasionally appeared in atypical spatial relations to old basal bodies. As a probable consequence of this defect, the fidelity of cytoplasmic inheritance of preexisting ciliary row number, which was demonstrated to be considerable in normal clones, was reduced in the abnormal clones.