Sex determination: a hypothesis based on noncoding DNA.

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Abstract
Certain recent models of sex determination in mammals, Drosophila melanogaster, Caenorhabitis elegans and snakes are examined in the light of the hypothesis that the relevant genetic regulatory mechanisms are similar and interrelated. The proposed key element in each of these instances is a noncoding DNA sequence, which serves as a high-affinity binding site for a repressor-like molecule regulating the activity of a major sex determining gene. In several eukaryotes, certain DNA sequences that are sex-determining are noncoding, in the sense that they are not the structural genes of a sex-determining protein. In some species these noncoding sequences are present in one sex and absent in the other, while in others their copy number or accessibility to regulatory molecules is significantly unequal between the 2 sexes. This inequality determines whether the embryo develops into a male or a female.