TABLE 3.

Crossovers observed in 91 IBM IRILs

	No. of crossoversa
Group I			Group IIb			No. of crossovers/μmc
Chromosome	BBxMM	MMxBB	Subtotal	BxMxB	MxBM		Subtotal	Total
1	375	383	758	38	29	67	825	17
2	247	260	507	37	28	65	572	14
3	272	284	556	25	31	56	612	16
4	251	245	496	28	25	53	549	15
5	244	265	509	29	21	50	559	16
6	168	161	329	18	16	34	363	12
7	214	223	437	30	20	50	487	17
8	222	208	430	14	20	34	464	16
9	208	184	392	9	18	27	419	16
10	162	155	317	21	22	43	360	16
Total	2363	2368	4731	249	230	479	5210

^a“x” indicates crossover position. B and M stand for B73 and Mo17 alleles, respectively. Crossovers are classified into group I (a single crossover between two pairs of markers from the same parent, i.e., BBxMM or MMxBB) and II (two crossovers flanking a marker, i.e., BxMxB or MxBxM). Within each group, the ratios of the two types (i.e., BBxMM vs. MMxBB or BxMxB vs. MxBxM) are not significantly different from the expected 1:1. The special cases of BxMM and MxBB that can occur at the ends of chromosomes were classified as group I events.

^bBecause there are opportunities for crossovers in multiple generations during the development of IRILs, group II events need not have arisen via double crossovers.

^cNumber of crossovers chromosome per length of pachytene chromosome. Pachytene chromosome lengths are from the inbred KYS (Anderson et al. 2003).