Interstitial deletions of repetitive DNA blocks in dicentric human Y chromosomes.

Cytogenetic analysis of aberrant human Y chromosomes was done by fluorescence in situ hybridization (FISH) with Y specific repetitive DNA probes. It revealed an interstitial deletion of different DNA blocks in two dicentric chromosome structures. One deletion includes the total alphoid DNA structure of one centromeric region. The second deletion includes the total repetitive DYZ5 DNA structure in the pericentromeric region of one short Y arm. Both dicentric Y chromosomes were iso(Yp) chromosomes with break and fusion point located in Yq11, the euchromatic part of the long Y arm. Their phenotypic appearance was "abnormal", resembling small monocentric Yq-chromosomes in metaphase plates. Mosaic cell lines, usually included in karyotypes with dicentric Y chromosomes, were not observed. It is assumed that both deletion events suppress the kinetochore activity in one Y centromeric region and thus stabilize its dicentric structure. Local interstitial deletion events had not been described in dicentric human Y chromosomes, but are common in dicentric yeast chromosomes. This raises the question of whether deletion events in dicentric human chromosomes are rare or restricted to the Y chromosome or also represent a general possibility for stabilization of a dicentric chromosome structure in human.