Table 1.

CO occurrence and distribution in 57 meioses by chromosome

Parameter	Chromosome
	I	II	III	IV	V
Meioses with 0 CO observed, n	0	5	0	2	0
1 CO	4	38	9	43	19
2 COs	26	14	36	12	32
3 COs	19	0	9	0	5
4 COs	3	0	2	0	1
5 COs	4	0	1	0	0
6 COs	1	0	0	0	0
Meioses without COs (upper arm), n*	2	47†	9	56†	12
Meioses without COs (lower arm), n*	3	13	11	6	10
Maximum separation of COs, cM‡	84	58	81	58	77
COs observed (total), n	151	66	121	67	103
CO per megabase (Mb)§	0.092	0.058	0.162	0.055	0.107
Average no. COs per meiosis	2.7	1.2	2.1	1.2	1.8
Meioses with COs on only two chromatids, n	11	41	17	47	24
Meioses with COs on only three chromatids, n	24	7	26	7	19
Meioses with COs on all four chromatids, n	22	4	14	1	14
Average no. recombinant chromatids per meiosis	3.2	2.1	2.9	2.1	2.8
COs observed, n/COs expected, n (12)	1.14	0.87	1.41	0.69	0.84

COs were defined as reciprocal exchanges between two homologous chromatids.

*Arms were defined by the calculated centromere positions (Fig. 3).

^†Markers used to measure COs on chromosomes II and IV did not span the rDNA (12).

^‡Map distances were derived from a male-specific meiotic map (Fig. 3).

^§Average number of COs observed/chromosome size, calculated by using 28.7, 20, 13.1, 21.5, and 16.9 Mb for chromosomes I–V, respectively (28). For chromosomes II and IV, elimination of the rDNA from the calculation yields 0.068 and 0.063 CO/Mb, respectively.