Table 1.

Spontaneous and MNU-induced mutation frequencies for BC-1 controls, BC-1/MSH2^+/− and BC-1/MSH2^−/−

Tissue	Animal	BC-1 controls
		Untreated control animals			MNU-treated animals
		Total pfu	No. of mutants	Mutation frequency, ×10−5	Total pfu	No. of mutants	Mutation frequency, ×10−5
Small intestine	a	286,860	11	3.8	211,384	106	50.1
	b	261,540	4	1.5	191,800	102	53.2
	c	265,320	11	4.1	179,380	210	117.1
	Mean			3.1 ± 1.4			74 ± 38
Thymus	a	292,890	13	4.4	206,580	13	6.3
	b	264,180	8	3.0	203,720	65	31.9
	c	285,680	5	1.8	195,680	54	27.6
	Mean			3.1 ± 1.3			22 ± 14
Heart	a	244,960	10	4.1	202,620	29	14.3
	b	229,400	30	13.1	158,220	14	8.8
	Mean			8.6 ± 6.4			12 ±  4

Tissue	Animal	BC-1/MSH2+/−
		Untreated control animals			MNU-treated animals
		Total pfu	No. of mutants	Mutation frequency, ×10−5	Total pfu	No. of mutants	Mutation frequency, ×10−5
Small intestine	a	253,560	7	2.8	217,044	91	41.9
	b	299,340	7	2.3	217,660	78	35.8
	Mean			2.6 ± 0.4			39 ± 4
Thymus	a	259,080	5	1.9	201,550	61	30.3
	b	257,900	17	6.6	214,040	39	18.2
	Mean			4.3 ± 3.3			24 ± 9

Tissue	Animal	BC-1/MSH2−/−
		Untreated control animals			MNU-treated animals
		Total pfu	No. of mutants	Mutation frequency, ×10−5	Total pfu	No. of mutants	Mutation frequency, ×10−5
Small intestine	a	282,640	93	32.9	221,340	330	149
	b	269,980	99	36.7	200,420	687	343
	c	246,440	80	32.5	202,640	613	303
	Mean			34 ±  2			265 ± 102
Thymus	a	300,460	89	29.6	203,420	394	194
	b	295,020	166	56.3	214,920	652	303
	c	281,640	155	55.0	200,840	566	282
	Mean			47 ± 15			260 ±  58
Heart	a	215,740	34	15.8	252,360	64	25.4
	b	96,080	16	16.7	88,660	42	47.4
	c	196,980	54	27.4	94,480	60	63.5
	Mean			20 ±  6			45 ±  19

pfu, plaque forming units.