Elimination of spontaneous and chemically induced chromosome aberrations in mice during early embryogenesis.

NMRI mice (female female) were treated with 0.25 mg/kg body weight Trenimon (2,3,5-triethyleneiminobenzoquinone-1,4) in the preovulatory phase just before ovulation. Then they were mated with untreated males. The female mice were dissected 45 h after application of this mutagen. The preimplantation embryos, being in a 2-cell stage, were flushed out of the oviduct and cultured in vitro for 60 h. Of the cultured embryos 87.7% reached the blastocysts stage in the control series, whereas only 49.7% did so in the experiments. Some of the females were dissected on the 14th day post conception (p.c.) and the number of dead and living implants was determined. Furthermore, the 9.5- and 13.5-day-old embryos were cytologically investigated, to determine the frequency of chromosomal aberrations. Of the unfertilized oocytes 76.2% deriving from mice treated with 0.25 mg/kg Trenimon, were aberrant in the stage of metaphase II (Röhrborn and Hansmann, 1971). Comparing Röhrborn's and Hansmann's results (1971) to our own findings a continuous elimination of chromosome aberration is clearly to be seen during early embryogenesis. The biological selection takes place in the pre- as well as in the early and late postimplantative phase.