Sex chromosome-specific DNA sequences.

Genetic linkage analysis using restriction fragment length polymorphisms is feasible for a human sex-linked disorder even when the primary gene product is not known. Distant probes localise a defect, while more closely linked clones can be used either for unambiguous carrier detection, particularly if sequences on both sides of the gene defect can be isolated, or for prenatal diagnosis using DNA obtained in early pregnancy by trophoblast sampling. Furthermore, with the isolation of sex chromosome libraries and the development of molecular biological techniques, a greater understanding of the basis of gonadal differentiation and sex-linked diseases should be achieved in the next few years.