The Regulatory Hierarchy Controlling Sex Determination And Dosage Compensation IN

Abstract

This chapter compares and contrasts various aspects of sex determination and dosage compensation processes in Caenorhabditis elegans with their counterparts in Drosophila melanogaster and mammals. This chapter emphasizes two points. The first is that sex determination strategies that initially appear to be quite different may not in fact be so different after all. At face value, the sex-determining mechanism of C. elegans, in which the X/A ratio serves as the primary sex-determining signal, seems extremely unlike that found in mammals, where a dominant sex chromosome (the Y chromosome in males) is the primary determinant of sex. Moreover, C. elegans can be readily interconverted from the XX hermaphrodite-XO male state to a ZW female-ZZ male state, in which sex is determined by a dominant sex chromosome (the W chromosome in females), by using a combination of dominant and recessive mutations at a single sex-determining locus. Evolutionary mechanisms by which this type of change might occur, as well as examples from other organisms in which populations have been changed from one sex-determining system to another under selective pressure, have been discussed extensively in the chapter. When sex determination is considered in a broader context, as a model for studying the fundamental processes in developmental biology, the field is enriched by the finding of such diversity because it increases the number and types of developmental strategies that may be discovered and elucidated.