Table 9.

Chr21 distribution of Ψg and Alu sequences in intergenic regions and introns

	Total	Intergenic	Intron	Overlapping with exons
Ψg counts	53	44	9	0
Alu counts	12,168	8,250	3,884	34
Length of region, kb	33,092	24,851	8,241
Marker density, count per kb
Ψg	0.0016	0.0018	0.0011
Alu	0.3677	0.3321	0.4713

There are 34 Alu sequences overlapping with exons. Eight of 34 overlap with internal exons and 26 overlap with boundary exons.