Chimeric transcript event types. A) A fusion in which the first two exons of gene A are joined to the last two exons of gene B. B) A partial tandem duplication in which the second exon of gene A is duplicated. NCEJ marks the non-canonical exon junction between the two copies of exon A2. C) An internal tandem duplication in which a portion of the second exon of gene A is duplicated, internal to the exon. D) A circular transcript involving only the second exon of gene A. Note that it contains the same A2-A2 NCEJ as the PTD in (B).