Homologous early replication patterns of the distal short arms of prometaphasic X and Y chromosomes.

Replication studies on prometaphasic human sex chromosomes reveal a distinct early replicating segment on both distal Xp ad Yp. These segments correspond to high resolution bands Xp22.3 and Yp11.3. The findings demonstrate synchronous replication of these parts of the sex chromosomes and correspond to the comparatively long stretches of Xp and Yp that participate in a synaptonemal complex. Furthermore these observations are compatible with Polani's view that suggests homologous segments with similar genetic information on both sex chromosomes (Polani 1982).