Does one gene determine whether a C57BL/6J-YPpos mouse will develop as a female or as an hermaphrodite?

Two studies were conducted to further our understanding of the inherited co ndition in mice known as C57BL/6J-Y-POS (B6-Y-POS) sex reversal. One study determined what proportion of B6 XYPOS mice develop as females or hermaphro dites. We found that 75% develop as females and the remainder develop as he rmaphrodites regardless of whether the analysis is conducted at 14.5-16 day s of embryonic development (based on gonad phenotype) or at weaning (based on the appearance of external genitalia and presence of mammary-associated yellow pigmented hair). We also found that 75 % of the gonads in B6 XYPOS m ice develop as ovaries and the remainder develop as ovotestes; none develop as a testis. We conclude that if any testicular tissue develops, sufficien t testosterone is produced to cause at least some masculinization of the ex ternal genitalia. The second study tested the hypothesis that development o f testicular tissue in B6 XUPOS mice is due to the presence of a POS-derive d gene, whereas B6 homozygosity of this gene guarantees ovarian development . The results did not support the POS gene theory. Therefore, we conclude i t is a matter of chance that 75 % of B6 XYPOS mice develop as females and 2 5 % develop as hermaphrodites. (C) 2001 Wiley-Liss, Inc.