[Spontaneous chromosome aberrations in the oogenesis of laboratory rats]

Cytological preparations were made by Tarkovsky's method from 2335 rat oocytes obtained after an induced superodulation. The chromosomes could be counted exactly in 861 oocytes. In 797 oocytes (92.7%) euploidy (metaphase II with 21 chromosomes) and in 64 oocytes (7.5%) aneuploidy was found. 60 oocytes were hypoploid, but only 4 oocytes (0.4%) were hyperploid (with 22 chromosomes). Hypoploidy can often be due to the presence of artefacts. Probably the rate of spontaneous aneuploidy in rat oogenesis is about 0.8%, this being significantly lower than the rate of spontaneous aneuploidy in mice oogenesis.