Evidence of prenatal heterosis relating to x-ray induced congential anomalies.

Abstract

Embryonic mice at 8.5 days gestation from pure C57 and CFl strains and their hybrids were x irradiated to 200 r to determine whether or not prenatal heterosis was manifest. Critenia were the number of normal, resorbed, dead, or anomalous mice seen at 18.5 days in the hybrids as compared with the pure lines. The hybrids at 8.5 days exhibited some degree of heterosis based upon the higher percentage of normal fetuses and the lower percentage of resorptions when comparisons were made with the pure strain parental stocks. For heterosis to be manifest, the hybrids had to overcome the severely deleterious effect of the presence of C57 genes as indicated by the 90% resorptions among this parental stork and only 30% in the hybrids, whereas the CFl showed 39%. Thus there is evidence of more than mere dominance of the more resistant strain genes which leads to heterosis at least by the time of organogenesis. The heterosis for the embryo results in better survival and thus better survival also of the x- irradiation-produced congenital anomalies. (auth)