Table 2.

The observed and expected distributions of intron positions and results of χ²-test for biased intron distribution for each genome

Species	Total CDSs	Observed equally distributed	Expected 5′-biased	Observed 5′-biased	Expected 3′-biased	Observed 3′-biased	χ2-valuea	χ2-valueb	Ratio of 5′-to 3′-biased
C.familiaris	16 827	2501	6404	7214	6404	5594	204.9	118.9	1.3
G.gallus	14 250	2558	5446	5936	5446	4957	88	48.7	1.2
H.sapiens	20 552	3334	7120	8362	7120	5879	432.9	256.6	1.4
R.norvegicus	21 053	3822	7449	8954	7449	5944	608.1	385	1.5
P.troglodytes	21 673	3711	7987	8787	7987	7187	160.3	84.8	1.2
M.musculus	23 913	4035	8006	9535	8006	6478	583.6	364.7	1.5
A.mellifera	5798	1370	2130	2506	2130	1755	132.4	103.8	1.4
C.elegans	11 754	2769	4336	5676	4336	2996	828.2	712.1	1.9
A.thaliana	26 258	3799	8410	8749	8410	8072	27.2	0.1	1.1
D.melanogaster	13 181	1986	4172	5354	4172	2991	669.1	290	1.8
A.gambiae	1953	271	642	689	642	594	7	0.4	1.2
S.pombe	1688	101	333	528	333	138	228.4	137.9	3.8
P.falciparum	567	21	144	199	144	89	42	2.5	2.2
Y.lipolytica	6058	6	314	582	314	46	457.5	35.9	12.7
D.hansenii	6697	2	166	304	166	29	227.1	7.1	10.5
E.cuniculi	1468	1	6	13	6	0	13	–	–
S.cerevisiae	4491	2	126	239	126	12	205.3	–	19.9
E.gossypii	4708	1	108	200	108	15	159.2	–	13.3
K.lactis	5217	0	63	119	63	7	99.6	–	17
C.glabrata	5255	1	40	75	40	6	58.8	–	12.5
G.theta	214	0	8	15	8	0	15	–	–

^aχ²-test was performed with df = 1, χ²-value is 10.83 (6.63) at an α level of 0.001 (0.01).

^bThis χ²-value is calculated when excluded from all of CDSs with only single intron.