Four-way Venn diagram illustrating the overlap of genes expressed in all pools at different stages of erythroblast maturation. (A) Overlap of genes expressed at successive stages of erythroblast maturation. (B) Overlap of highly expressed transcripts at successive stages of erythroblast maturation. Expression cut-offs are selected with the caveat that expression measurements on array platforms are relative and prone to influence by physical hybridization factors. Numbers of transcripts are shown that exceeded an expression level of 100 in all 3 triplicates at each stage. A total of 12 094 genes represented on the HGU133_plus_2.0 arrays were absent from all stages studied. Numbers of transcripts that exceeded an expression level of 500 in all 3 triplicates at the combinations of stages indicated. A total of 4640 genes are common to all stages, whereas other genes show a more stage-specific expression pattern; for example, 511 are only present at the Late-E stage (red). When the expression cut-off is increased to 500, the number of transcripts meeting that criteria at all stages drops to 1144, and 396 genes exceed an expression level of 500 at the Late-E stage only.