Pericentric inversion of the human Y chromosome has been reported infrequently but it is known to be an inherited anomaly. Several Harris, 1970) that both sexes were affected; the parents were first cousins, and the affected boys and their normal father had a pericentric inversion of the Y chromosome. The present study was done in an attempt to find the origin of the unusual Y chromosome. Family StudyThe family, whose pedigree is shown in Fig. 1 (Fig. 4). There was little difference in the number of interphase nuclei showing a Y-spot; the highest score was 22% positive and the mean score of all buccal and lymphocyte preparations was 7%.