Table 2

Summary of the genomic analysis of the 21q11-21 region

Genomic size of 21q11-21∼20 Mb
Microdissection libraries specific for 21q11-21MA, MB, SA, SB
Independent, individual clones in the libraries>40,000 (mean insert size 300 bp)
Cloned genomic size for 21q11-21>12 Mb
No. of microclones analyzed>2,500 by repetitive sequence screening
>1,000 by Southern hybridization
>400 (>120 kb DNA) by DNA sequencing
Highly repetitive sequences in 21q11-2146%
Moderately repetitive sequences in 21q11-2124%
Low-copy sequences in 21q11-2118%
Unique sequences specific for 21q11-2112%
Methylation in 21q11-21 (HpaII sites)>90%
Conserved microclones (cross-hybridizing to rodents)19% (76/400) in unique and low-copy microclones
GC content in unique and low-copy microclones<40%