[Cytogenetic analysis of the 1-st cleavage division of rat embryos].

The chromosome number in 174 zygotes on the stage of the 1st cleavage division was counted. In 113 zygotes (64.94%) euploidy (metaphase with 42 chromosomes) and in 57 zygotes (32.77%) aneuploidy was found. Frequencies of spontaneous chromosomal aberration were 14.93%. 33 zygotes were hypoploid, 6 (3.44%)--hyperploid (with 43 and 46 chromosomes), and 3 (5.76%)--polyploid, 4 zygotes (2.29%) had structural anomalies of chromosomes. Hypoploidy may be often due to artifacts. Superovulation induced by gonadotrophin results in an increased polyspermia.