Arrangement of DYZ1 and DYZ2 repeats on the human Y-chromosome: a case with presence of DYZ1 and absence of DYZ2.

The composition of Yq-heterochromatin is dominated by the two repetitive sequences DYZ1 (4000 copies) and DYZ2 (2000 copies). Probes derived from these sequences can be used for sex determination and the structural analysis of aberrant Y-chromosomes. Using such probes Schmid et al., have recently proposed a regular interspersion of the two sequences in a ratio of 2:1 over the entire Yq12 chromosome region. By Southern analysis we investigated the DNA of a normal male, cytogenetically negative for Yq-heterochromatin. Applying the same probes as used by Schmid et al., only a small amount of DYZ1 material could be detected. The case presented indicates the presence of DYZ1 only in the Yq11-Yq12 junction region and excludes DYZ2 from any function relevant for normal male development.