Cytogenetic and biochemical investigations on fibroblast cultures and clones with one and two active X chromosomes of a 69,XXY triploidy.

Bromodeoxyuridine replication patterns showed that fibroblasts from a 69,XXY triploidy carried either one or two early replicating X chromosomes. The activity of alpha-galactosidase A measured in single cells fell into two classes with a ratio of 1:2. Dilute plating produced clones of both types with the activity of alpha-galactosidase A corresponding to the number of active X chromosomes. To our knowledge, this is the first report on clones of a triploidy with different numbers of active X chromosomes, and on a gene-dosage effect of an X-linked gene using triploid cells with one active X as control.