TABLE 5.

 Distribution of zero-, one-, and double-crossover events in mer3 mutant strains

Relevant genotype	Interval	Result at a:
		30°C							23°C
		No. of events						Probability	No. of events						Probability
		Observed			Expected				Observed			Expected
		0-CR	1-CR	2-CR	0-CR	1-CR	2-CR		0-CR	1-CR	2-CR	0-CR	1-CR	2-CR
MER3	CAN1-URA3	191	282	60	251	189	71	4.1 × 10−14	187	282	68	247	192	75	3.7 × 10−13
	URA3-CAN1	206	284	44	266	185	65	1.7 × 10−16	177	289	72	241	194	78	1.1 × 10−14
mer3GD	CAN1-URA3	304	196	36	325	163	41	1.2 × 10−2	322	186	12	347	140	28	2.1 × 10−6
	URA3-CAN1	341	181	20	361	147	30	2.2 × 10−3	356	153	12	371	126	21	5.2 × 10−3
mer3KA	CAN1-URA3	331	195	20	355	153	33	1.1 × 10−4	327	157	40	333	151	34	5.0 × 10−1
	URA3-CAN1	347	173	20	364	144	28	9.7 × 10−3	374	140	12	385	120	19	4.9 × 10−2

^aTetrads obtained in Table 2 were examined. The observed number of zero-, one- and double-crossover (0-, 1-, and 2-CR, respectively) events in an interval was derived from the number of PD, TT, and NPD events as 0-CR = PD − NPD, 1-CR = TT − 2NPD, and 2-CR = 4NPD, since only one class gives NPDs among four classes of 2-CR tetrads, assuming no chromatid interference. The expected number of 0-, 1-, and 2-CR events was predicted by a Poisson distribution from the frequency of crossing over observed in Table 2. Chi-square tests were performed to express the likelihood that the difference between the observed and expected patterns was attributable to chance.