Table 2.

The Frequency of Recombination Events Along Chromosome 21 During Maternal Meiosis Among Mothers of Different Age Groups

				No. (frequency) of subjects with:
Stage of error	Maternal age group	Mean maternal age (years±SD)	Sample size	0 observed recombination	1 observed recombination	2 observed recombinations
MI	Young (≤28)	25.00±3.65	32	25 (0.78)	6 (0.19)	1 (0.03)
	Middle (29–34)	31.60±2.07	24	19 (0.79)	4 (0.17)	1 (0.04)
	Older (≥35)	37.75±1.70	26	21 (0.80)	5 (0.20)	0
MII	Young (≤28)	28.33±0.57	3		2 (0.66)	1 (0.33)
	Middle (29–34)	32.00±2.00	5		3 (0.60)	2 (0.40)
	Older (≥35)	39.25±3.30	5		4 (0.80)	1 (0.20)

MI, first meiotic division.

MII, second meiotic division.