title: Two types of sex determination in a nematode.
abstract: Sex in the nematode Caenorhabditis elegans is normally determined by a genic balance mechanism, the ratio of X chromosomes to autosomes, so that XX animals are self-fertilizing hermaphrodites and X0 animals are males. However, recessive mutations of the autosomal gene tra-1 III cause both XX and X0 animals to develop into males, and a linked dominant mutation causes both XX and X0 animals to develop into females. Here I show that these two kinds of mutation are allelic, and that stable mutant strains can be constructed in which sex is determined not by X-chromosome dosage but by the presence or absence of a single active gene. In these strains the autosomes carrying the tra-1 locus are in effect homomorphic Z and W sex chromosomes, and the sexes are homogametic ZZ males and heterogametic ZW females, in contrast to the wild-type arrangement of homogametic XX hermaphrodites and heterogametic X0 males.
mesh_terms: D000483:Alleles; D000818:Animals; D002107:Caenorhabditis / Q000235:genetics*; D005260:Female; D005799:Genes, Dominant; D005816:Genetic Complementation Test; D008297:Male; D009154:Mutation; D012730:Sex Chromosomes / Q000502:physiology; D012732:Sex Determination Analysis