Table 3.

Analysis of natural and induced polymorphisms

polymorphism		natural rate b	EMS		Az-MNU
type	change a		ob c	ex d	ob	ex
transitions	GC->AT	0.32	19	8.53	20	9.48
	AT->GC	0.35	3	9.48	6	10.53
transversions	GC->TA	0.09	1	2.33	0	2.59
	GC->CG	0.07	0	1.84	0	2.05
	AT->TA	0.09	4	2.30	2	2.55
	AT->CG	0.09	0	2.52	2	2.80
Statistical analysis e
transitions	GC->AT	0.32	19	8.53	20	9.48
	AT->GC
transversions	GC->TA
	GC->CG	0.68	8	18.46	10	20.52
	AT->TA
	AT->CG
Probability			0.0067		0.0042

^a GC->AT is expected from G base-alkylating mutagens. Changes in bold are rare to uncommon in EMS- or MNU-treated organisms (see references in text). ^b calculated from 62,000 natural SNPs of rice. ^c observed. ^d expected for natural polymorphisms. ^e P of the null hypothesis that the observed changes are natural polymorphisms was calculated with Fisher Exact test for each for 2-by-2 table of data from the EMS (ethyl methanesulfonate treatment) and Az-MNU (sodium azide – methyl nitrosourea treatment). See Discussion and Methods for details.