A cytogenetic investigation of inherited true hermaphroditism in BALB/cWt mice.

A predictably high incidence of true hermaphroditism (3%) among fetal BALB/cWt mice provided the opportunity for studying the cause of inherited hermaphroditism. G-banded liver metaphase chromosomes were analyzed from 20 fetal hermaphrodites and from 15 normal female and male littermate controls. All hermaphrodites and seven males were chromosomal mosaics, i.e. XO/XY or XO/XY/XYY. In each mosaic fetus there were more XO than XYY cells. From these findings we hypothesize that BALB/cWt hermaphrodites arise from non-disjunction and probable loss of the Y-chromosome during mitosis. Results from breeding experiments indicated that a defect in the BALB/cWt Y-chromosome per se accounts for its nondisjunction and loss. A significant relationship was found between the amount of ovarian tissue and the percentage of XO cells in mosaic fetuses. If all chromosomally mosaic (XO/XY and XO/XY/XYY) individuals are considered, ovarian tissue was formed if there was 24% or more XO cells in an individual. If only hermaphroditic individuals are considered, ovarian tissue was formed if there were 44% or more XO cells. Finally, we found that the distribution of ovarian and testicular tissue within an ovotestis of BALB/cWt hermaphrodites was not random: ovarian tissue was situated at both ends or only at the cranial end; in only one case was ovarian tissue situated in the center flanked by testicular tissue. We suggest that such nonrandom distribution of ovarian and testicular tissue argues against the hypothesis that the organization of testicular tissue is dependent only on the presence of H-Y antigen.