Three large, probably tandem duplications (Dps) on the Xchromosome were isolated as semi-dominant suppressors of the masculinizing her-l (
n695sd) allele. They feminize XO animals more strongly than any other known X Dps, causing variable hermaphrodite gonad, germ line, and vulval development. One copy of one of these Dps (e.g.
ct31) suppresses completely the masculinization of XX animals caused by either her-l (
n695) or the stronger gain-of-function allele her-l(ylOI) . By comparison, one copy of the large X Dp mnDpl O(X:I) does not ferninize XO males; its effect on the phenotype of her-l (yl Ol) XX animals is being determined. Endpoints of Dps were mapped by quantitative Southern blot analysis and visualized by in situ hybridization. Each of the feminizing Dps includes about 40%+-5% of the X with endpoints to the right of
sup-28 and to the left of
lin-15. mnDplO also includes about 40% +5% of X, extending from a point to the right of
lin-14 to the right end of the chromosome. The calculated X/A ratio in XO animals carrying one copy of any one of these four Dps is . 67 - .72, in the previously established intersexual range (1). If they are no larger than mnDplO, then the feminizing Dps must include specific feminizing elements not included in mnDplO. One obvious candidate would be the
sdc-2 gene. Loss of
sdc-2 function increases the level of her-l transcripts in XX animals (2); gain of function that might result from an additional copy of
sdc-2 could feminize by repressing her-l transcription. Northern blot analysis confirmed marked reduction of her-l (
n695) transcripts in XX animals carrying a feminizing Dp. To determine whether increased
sdc-2 dose could account for feminization by
ct31, the strong loss-of-function allele
sdc-2(ylS) was introduced in trans to
ct31 in ylOl hermaphrodites. This strain ( 2 copies of
sdc-2) showed the same degree of feminization as the parent strain not carrying ylS (3 copies of
sdc-2), indicating that the differences between the feminizing Dps and mnDplO are not the result of
sdc-2 copy number differences. We are exploring the possibility of other feminizing loci in this region of X.