A cytogenetic survey of an institution for the metnally retarded. III. Q-Band chromosome heteromorphisms.

Heteromorphisms of chromosomes 3, 4, 13-15, 21-22, and Y were studied in a population of 374 mentally retarded patients from diverse ethnic groups. A significant variation in the size of the Y chromosome was found among different racial groups, those of the Orientals and Filipinos being larger than those of the Caucasians or Polynesians. No other significant variation was found among the different racial groups, although suggestive differences were seen in bands 3 cen, 13p3, and 14p3. Band 13 cen/pl was significantly larger in the category of socio-familial retardation than in the other two categories. However, as the significance was at the 0.05% level and as this was the only heteromorphism whose distribution was different among the three categories of mental retardation, we assign little importance to this observation.