Human sex-chromosome-specific repeats within a region of pseudoautosomal/Yq homology.

Several categories of human X-Y homologous DNA sequences have been recognized. We report that a locus (DXYS77) approximately 14 kb distal to the pseudoautosomal boundary (PAB) is 93% identical in nucleotide sequence to a locus (DYS148) on the long arm of the Y chromosome (Yq). Within this segment of pseudoautosomal/Yq homology we identified a member of a family of repeats that are concentrated in Xp22.3 and in the euchromatic portion of the Y chromosome. The repeat sequence structure--a dimer bounded by short terminal repeats--is reminiscent of retroposons derived from RNA polymerase III transcripts.