Abstract
Recessive mutant alleles at the autosomal dpy-21 locus of C. elegans cause a dumpy phenotype in XX animals but not in XO animals. This dumpy phenotype is characteristic of X chromosome aneuploids with higher than normal X to autosome ratios and is proposed to result from overexpression of X-linked genes. We have isolated a new dpy-21 allele that also causes partial hermaphroditization of XO males, without causing the dumpy phenotype. All dpy-21 alleles show hermaphroditization effects in XO males that carry a duplication of part of the X chromosome and also partially suppress a transformer (tra-1) mutation that converts XX animals into males. Experiments with a set of X chromosome duplications show that the defects of dpy-21 mutants can result from interaction with several different regions of the X chromosome. We propose that dpy-21 regulates X chromosome expression and may be involved in interpreting X chromosome dose for the developmental decisions of both sex determination and dosage compensation.