Expression patterns for major transcripts . ( a ) Percentage of genes with recurrent and non-recurrent major transcripts. Changes in the identity of major transcripts across samples were quantified with switch events. (b) Concept of switch event. A gene is considered to be involved in a switch event if we detect two different dominant major transcripts in two different samples. If the dominant transcripts involved in the switch are expressed above 5 FPKM, while the minor ones are expressed below 1 FPKM, we define the event as a strong switch.