Table 1

Number of CpG islands in chromosomes 21 and 22

Category212221 + 22
5′ region57138195
Exon334423757
Alu repeats2,5205,1317,651
Unknown2,1283,3315,459
Total5,0399,02314,062
  • CpG islands were categorized into four categories in this order: “5′ region” included at least the first coding exon of a known gene and might or might not include downstream introns, exons and Alus. An “Exon” CpG island did not include a known first coding exon and possibly included intronic and Alu sequences. An “Alu” did not include a known exonic sequence. “Unknown” sequences did not satisfy any of the above criteria.