A number of individuals with aberrant Y chromosomes have been tested for the presence of Y-chromosome-specific reiterated DNA. These studies locate Y-chromosome-specific reiterated sequences on the long arm of the Y chromosome. Correlation with phenotype and other known Y chromosome markers establish that the Y-chromosome-specific reiterated DNA discussed here has no evident role in male determination.

Increased production of fetal hemoglobin (HbF) was observed in a patient with sickle cell anemia treated with 5-azacytidine. Each of four courses of therapy resulted in a rapid and prolonged increase in the percentage of HbF containing reticulocytes (F reticulocytes) and HbF containing erythrocytes (F cells). The percentage of HbF in peripheral blood rose from 1.8 to 8.9%. The rise in HbF production was accompanied by an increase in peripheral blood hemoglobin concentration from 8 to 12 g/dl and an increase in mean erythrocyte volume. Treatment with 5-azacytidine resulted in hypomethylation of total genomic and a Y-chromosome-specific DNA fragment isolated from both peripheral blood and bone marrow. Of 15 restriction enzyme sites around the gamma-delta-beta-globin gene complex, only 2 became hypomethylated: one 107 bases 5' to the gamma G and the other 107 bases 5' to the gamma A globin genes.

During adult life, the quantity of fetal hemoglobin (HbF) present in F cells--that is, rare erythrocytes which are reactive with rabbit antiserum to human HbF during microscopic immunodiffusion--is sufficient to account for all of the small quantity (less than 0.7 percent) of HbF normally present in whole blood. Thus, erythrocytes are normally heterogeneous with respect to the presence of HbF.

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