Abstract
DNA sequence data have been obtained from three clones derived from the human X chromosome which contain evolutionarily conserved sequences. Primers have been designed which enable these loci to be defined as sequence-tagged-sites (STS’s). The assignment of one of the loci, DXF34S1, has been refined to Xp11.21-cen, thus limiting the novel pericentromeric segment of homology defined by this locus to the extreme proximal region of Xp.