ISOLATION OF DOMINANT XO-FEMINIZING MUTATIONS IN CAENOHABDITIS-ELEGANS - NEW REGULATORY TRA-ALLELES AND AN X-CHROMOSOME DUPLICATION WITH IMPLICATIONS FOR PRIMARY SEX DETERMINATION

A strain of Caenorhabditis elegans was constructed that permits select ion of dominant or sex-linked mutations that transform XO animals (nor mally male) into fertile females, using a feminizing mutation, tra-2(e 2046gf), which by itself does not sexually transform XO males. Twenty- three mutations were isolated after chemical mutagenesis and found to fall into both expected classes (four dominant tra-1 mutations and eig ht recessive xol-1 mutations) and novel classes. The novel mutations i nclude 10 second-site mutations of tra-2, which are called eg mutation s, for enhanced gain-of-function. The tra-2(gj, eg) alleles lead to co mplete dominant transformation of XO animals from fertile male into fe rtile female. Also isolated was a duplication of the left end of the X chromosome, eDp26 which has dominant XO lethal and feminizing propert ies, unlike all previously isolated duplications of the X chromosome. The properties of eDp26 indicate that it carries copies of one or more numerator elements, which act as part of the primary sex-determinatio n signal, the X:A ratio. The eDp26 duplication is attached to the left tip of the X chromosome in inverted orientation and consequently can be used to generate unstable attached-X chromosomes.