Expression of Per2 in AML. Expression levels of Per2 were measured in light density, mononuclear bone marrow samples (enriched for less differentiated, dividing cells) from 9 healthy donors (Healthy) and 21 patients with AML. The results are expressed in arbitrary units as a ratio of the Per2 transcripts to GAPDH transcripts (each value represents the mean of 3 measurements of the sample).