Studies on the inheritance of vaginal septa in mice, a trait with low penetrance

Longitudinal vaginal septa were found in 1-3% of females of the BALB/cBy and C57BL/6By inbred strains and their F1, F2 and backcross hybrids. In the CXBJ recombinant-inbred strain over half the females were affected, showing that the parental strains differed at a minimum of 2 loci that increased the risk of septa. Crosses involving CXBJ mice showed that susceptibility could be transmitted by the male parent and suggested that the different genotypes producing low penetrance could be identified. Subline differences in C57BL were marked, the incidence ranging from 1% in C57BL/6By to about 26% in two lines congenic with C57BL/10ScSn. No association was found between incidence and H-2 histocompatibility type. Imperforate vagina occurred at a low frequency in 4 stocks in which septa were regularly found. The minor anomaly was about 15 times more likely than the malformation.