POLYMER GENOMICSchr20·hg38·64.4 Mb
Atlas
Open chr20 in viewer Chromosome 20
The first metacentric human chromosome to be fully sequenced — a 64-megabase time capsule of mammalian evolution so perfectly conserved with the mouse that nearly every gene sits in the same order it occupied 87 million years ago.
Physical Properties
Length64.4 Mb
Centromeremetacentric
p-arm26.4 Mb
q-arm34.4 Mb
GC content44%
Genomic Features
Protein-coding genes544
Gene density8.4 / Mb
CpG islands7,739
EPIC v2 probes24,227
Notable
Largest geneMACROD2 (2.1 Mb)
Disease associations
Alagille syndrome
Albright hereditary osteodystrophy
MDS (ASXL1)
· Was the second chromosome fully sequenced (2001)
· ASXL1 is recurrently mutated in myeloid malignancies
· Contains multiple imprinted loci including GNAS
Genomic Architecture
Total interspersed repeats — ~44%, near the genome average
LINE-1 — Moderate representation (~16%)
Alu/SINEs — Moderate (~12%), substantially lower than chr19's extreme 26%
Deep Cuts
First metacentric, third overall — Chr20 was the third human chromosome to be fully sequenced (after chr22 in 1999 and chr21 in 2000), but the first metacentric. Chromosomes 22 and 21 are both acrocentric and small — chr20 proved that the sequencing me…
The gene therapy origin story — ADA-SCID on chr20 was the target of the first authorized human gene therapy trial in 1990. Ashanthi DeSilva, a 4-year-old with ADA deficiency, received her own T cells modified with a retroviral vector carrying a norm…
Fatal familial insomnia — the codon 129 switch — The PRNP D178N mutation at 20p13 causes two completely different lethal diseases depending on a single polymorphism at codon 129. D178N with Met129 = fatal familial insomnia (selective thalamic degeneration, untreatab…
§ Deep dive