chr3·hg38·198.3 Mb

Chromosome 3

The tumor suppressor chromosome: its short arm carries the densest concentration of cancer-critical genes in the human genome, including VHL, FHIT, RASSF1A, BAP1, SETD2, and PBRM1 — and losing 3p is the initiating event in clear cell renal cell carcinoma.

Physical Properties

Length198.3 Mb

Centromeremetacentric

p-arm90.8 Mb

q-arm104.6 Mb

GC content39.7%

Genomic Features

Protein-coding genes1,078

Gene density5.4 / Mb

CpG islands15,570

EPIC v2 probes56,811

Notable

Largest geneFHIT (1.5 Mb)

Disease associations

Von Hippel-Lindau disease

Renal cell carcinoma

Lynch syndrome

· 3p loss is frequent in renal cell carcinoma

· Contains the most common fragile site FRA3B

· Home to the FHIT gene spanning 1.5 Mb

Genomic Architecture

The 3p tumor suppressor corridor — An extraordinary concentration of tumor suppressor genes spans the short arm from 3p25 (VHL) through 3p21 (RASSF1A, BAP1, SETD2, PBRM1) to 3p14 (FHIT). Loss of 3p material — whether by deletion, translocation, or LOH …

FRA3B — the most fragile fragile site — The common fragile site FRA3B at 3p14.2 is the most frequently expressed fragile site in the human genome under aphidicolin-induced replication stress. It spans the FHIT gene, which at >1.5 Mb is among the largest gen…

Segmental duplications — Chromosome 3 has a moderate segmental duplication content. The pericentromeric region harbors duplications, but the chromosome is not as SD-enriched as chromosomes 1, 9, 15, 16, or 22.

Evolutionary History

Ancestral conservation — Chromosome 3 homologs are well-conserved across placental mammals. The ancestral eutherian karyotype reconstruction shows human chromosome 3 as a single syntenic block in most lineages (dog, horse, pig). In cat, the h…

Ancient synteny with chromosome 21 — Comparative painting studies reveal that chromosomes 3 and 21 were joined as a single chromosome in the common ancestor of most mammals. This 3/21 association is one of the most ancient and widely conserved syntenic b…

Deep Cuts

The "neoclassic quartet" — A 2001 PNAS commentary coined this term for the four 3p tumor suppressors (VHL, RASSF1A, FHIT, and a then-unidentified 3p21 gene) that cooperate in renal and lung carcinogenesis. Twenty years later, the quartet has ex…

FHIT is huge but its protein is tiny — FHIT spans 1.5 Mb of genomic DNA (one of the largest genes) but encodes a 147-amino-acid protein of just 16.8 kDa. The vast majority of the gene is intronic, and the introns are what make it fragile. Evolution has pla…

CCR5-delta32 and gene editing ethics — The CCR5 gene on 3p21 became the center of the largest bioethics controversy in genetics when He Jiankui used CRISPR to edit CCR5 in human embryos (the "CRISPR babies" of 2018). The intended phenocopy of the natural d…

§ Deep dive

The 3p tumor suppressor corridorAn extraordinary concentration of tumor suppressor genes spans the short arm from 3p25 (VHL) through 3p21 (RASSF1A, BAP1, SETD2, PBRM1) to 3p14 (FHIT). Loss of 3p material — whether by deletion, translocation, or LOH — is the single most recurrent chromosomal event in clear cell renal cell carcinoma (>90% of cases) and is also frequent in lung, breast, cervical, and head-and-neck cancers.

FRA3B — the most fragile fragile siteThe common fragile site FRA3B at 3p14.2 is the most frequently expressed fragile site in the human genome under aphidicolin-induced replication stress. It spans the FHIT gene, which at >1.5 Mb is among the largest genes. The fragility arises from late replication timing, AT-rich sequence composition (abundant AT-dinucleotide repeats), and a paucity of replication origins, causing replication fork stalling and breakage.

Segmental duplicationsChromosome 3 has a moderate segmental duplication content. The pericentromeric region harbors duplications, but the chromosome is not as SD-enriched as chromosomes 1, 9, 15, 16, or 22.

Repeat content~43% interspersed repeats. The FHIT gene at FRA3B is distinguished by extreme enrichment in AT-dinucleotide microsatellites relative to flanking non-fragile genes (e.g., PTPRG), explaining its preferential breakage under replication stress.

Gene desertsThe 3q arm contains several gene-poor intervals, including a ~3 Mb desert around 3q26.1. Conversely, 3p21 is gene-dense, creating a stark asymmetry in the distribution of functional elements along the chromosome.