POLYMER GENOMICSchr22·hg38·50.8 Mb
Atlas
Open chr22 in viewer Chromosome 22
"The smallest shall be first" — the first human chromosome fully sequenced, yet a hotspot for the most consequential structural rearrangements in medicine.
Physical Properties
Length50.8 Mb
Centromeresubmetacentric
p-arm13.0 Mb
q-arm35.8 Mb
GC content47.8%
Genomic Features
Protein-coding genes488
Gene density9.6 / Mb
CpG islands6,229
EPIC v2 probes18,221
Notable
Largest geneLARGE1 (664 kb)
Disease associations
DiGeorge syndrome
Neurofibromatosis type 2
Chronic myeloid leukemia
· First autosome fully sequenced (1999)
· 22q11.2 deletion (DiGeorge syndrome) — most common microdeletion
· The Philadelphia chromosome t(9;22) creates BCR-ABL1
Genomic Architecture
LCR22s — The 22q11.2 region contains extraordinary Low Copy Repeats — 26 different haplotypes of LCR22A alone, ranging 250 kb to >2,000 kb. Expanded specifically in the human lineage.
PATRRs — Palindromic AT-rich repeats predisposing to the recurrent t(11;22) translocation.
rDNA clusters — Short arm harbors tandem 45S rDNA arrays contributing to nucleolus formation.
Evolutionary History
Historical misnaming — Actually physically larger than chr21. Numbering preserved to avoid confusion with "Trisomy 21."
LCR22 expansion — Human-specific, post-dating human-chimpanzee divergence.
Deep Cuts
First chromosome sequenced — December 1999 by the Sanger Centre/Oklahoma/WashU/Keio. 11 gaps in the 33.4 Mb q-arm. Beat chr21 by a year.
Double translocation hotspot — Participates in two independent recurrent translocations — t(9;22) and t(11;22) — caused by entirely different sequence features. No other small chromosome has this.
The COMT paradox — In 22q11.2 deletion, a single remaining COMT allele determines dopamine phenotype absolutely — no second allele to buffer the effect.
§ Deep dive