Inversion of 'flourescent' segment in chromosome 3: a polymorphic trait.

The frequency of the 'inversion' of flourescent constitutive heterochromatin in chromosome 3 was the same in a sample of 370 retarded persons as in a sample of 222 mentally normal men. It can be concluded that this 'inversion' is not associated with mental retardation. This variant is more common (4%) in the Canadian population we studied than in samples reported by most other authors (0-1.7%). Possibly the founder effect could play a role in the differences. Two cases of homozygotes for this 'inversion' were identified.