a, Chromosome 2 RefSeq genes and CLIP tags from the neocortex of two mouse littermates (Brain A, 46,106 tags in 10,740 clusters; Brain B, 100,874 tags in 15,805 clusters). b, Cluster Density (#tags/cluster length; black) in the Grin1 transcript; c, (i) Grin1 E4 and (ii) E19 tags, one color per biologic replicate, predict Nova-dependent exon skipping and inclusion, respectively (experimental validation is shown).