Chromosome 3 is one of the 23 pairs of human chromosomes. People usually have two copies of chromosome 3, one inherited from each parent.
Chromosome 3 is a large autosome. MedlinePlus Genetics describes it as spanning about 198 million DNA base pairs and representing about 6.5 percent of the total DNA in human cells.
Structure
Like other human chromosomes, chromosome 3 has a short arm called p and a long arm called q. The centromere separates the two arms and helps the chromosome move correctly during cell division.
Locations on the chromosome are written using cytogenetic bands. For example, 3p25 refers to a region on the short arm, while 3q28 refers to a region on the long arm.
Genes
Chromosome 3 contains more than a thousand protein-coding genes, along with non-coding RNA genes and regulatory regions. Exact counts vary between genome annotation projects because gene models are updated over time.
Examples of genes on chromosome 3 include:
- MLH1, a mismatch repair gene linked to Lynch syndrome when pathogenic variants are inherited
- VHL, a tumour suppressor gene linked to von Hippel-Lindau syndrome
- SCN5A, which encodes a cardiac sodium-channel protein
- TP63, a transcription-factor gene involved in development of several tissues
- BAP1, a tumour suppressor gene linked to hereditary cancer predisposition
These examples show why chromosome 3 is relevant across cancer genetics, developmental biology, cardiology and inherited disease.
Chromosomal Changes
Disease can occur when part of chromosome 3 is missing, duplicated, rearranged or disrupted by a pathogenic gene variant.
Examples include:
- 3p deletion syndrome, caused by loss of genetic material from the short arm
- 3q29 microdeletion syndrome, caused by deletion of a segment on the long arm
- von Hippel-Lindau syndrome, caused by pathogenic variants in VHL
- Lynch syndrome in families with pathogenic MLH1 variants
- selected cardiac arrhythmia syndromes linked to SCN5A variants
Not every chromosomal difference has the same effect. The result depends on the genes involved, the size of the change, inheritance and the person's wider genetic background.
Role in Research
Chromosome 3 is studied in cancer, inherited developmental conditions, neurological conditions, eye disease and cardiac rhythm disorders. Genome sequencing and chromosomal microarray have made smaller deletions and duplications easier to identify.
Researchers also study chromosome 3 because several tumour suppressor genes are located there. Loss or inactivation of such genes can contribute to cancer development in particular tissues.
Testing
Different tests answer different questions. A karyotype can show large chromosomal rearrangements. Chromosomal microarray can detect smaller deletions or duplications. Gene panels and sequencing can identify smaller variants in individual genes.
The right test depends on the clinical problem being investigated.
See Also
References
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