Exon array detection of erythroid-specific beta spectrin mRNA 3′ end. (A) The exon structure of human beta spectrin transcripts in muscle versus erythroid cells, which express distinct 3′ terminal exons. (B) The splicing index of probe sets across the full length of the beta spectrin gene. Numbers along the horizontal axis represent probe set IDs. Positive values for the splicing index represent higher relative probe set expression in erythroblasts, whereas negative values indicate higher relative expression in muscle. The significant upward peak maps to the known erythroid-specific 3′ end, whereas the downward peak represents the muscle-specific 3′ end.