RESUMO
The frequency of consistent structural chromosome aberrations was determined for 108 fetuses (day 14 of gestation) from 20 female rabbits treated before conception with 90 micrograms/kg of streptonigrin (NSC-45383). The findings by karyotype analysis of 1.85% of the fetuses with consistent aberrations was compared with 6.32% frequency previously observed in 6-day (preimplantation) blastocysts from identically treated females and found to be significantly reduced. The interpretation of the findings is that the developmental events of implantation and placentation are effective in eliminating from further gestation the majority of the rabbit conceptuses with consistent structural chromosome abnormalities. The data are also discussed relative to the predictive nature of somatic cell chromosome damage in women of childbearing age being an estimator of risk of producing offspring with structural chromosome aberrations. The data show that preconceptional treatment of female rabbits with streptonigrin caused a shift in the cytogenetically determined sex ratio of the 14-day fetuses, but not of the 6-day blastocysts. The significant decrease in relative numbers of males observed is consistent with the induction of lethal mutations on the X chromosome. This finding is discussed in conjunction with the timing and parental specificity of X chromosome inactivation during mammalian embryonic development.