Table 1.

Conservation of U12 and U2 intron positions in orthologous human and Arabidopsis genes^a

	U2 intron positions		U12 intron positions		PFisher
	Shared	Variable	Shared	Variable
#conserved positions (U2–U12 mixed cases removed)	115	1371	20	115	0.008
#conserved positions, U2–U12 mixed cases are counted as variable introns	115	1391	20	135	0.003

^aTo eliminate potential artifacts caused by misalignment, all positions containing a deletion or insertion in the alignment within 5 adjacent position both upstream and downstream were discarded from calculation [16]; the results changed minimally when a stricter criterion was applied by eliminating 10 adjacent positions (data not shown).