triplication

Triplication is the genetic state in which three copies of a genetic segment exist in a cell where two copies are typical in diploid organisms. It can involve a small gene, a contiguous chromosomal segment, or an entire chromosome, and is a form of copy-number variation.

It most commonly arises through misalignment and unequal crossing over during meiosis or mitosis, or through replication-based mechanisms that generate extra copies. Triplication can be in tandem (three copies adjacent) or dispersed across the genome. It may occur in germline cells (inherited) or somatically (mosaic).

Dosage effects are central to its phenotype. A triplication can increase gene expression and alter cellular pathways, possibly leading to developmental delay, congenital anomalies, or predisposition to cancer, depending on the genes involved and the tissue context. Some triplications have mild or no apparent effects due to gene dosage tolerance or mosaicism.

Detection and interpretation rely on molecular cytogenetics and sequencing. Array comparative genomic hybridization (array CGH) and SNP arrays can identify CNVs; whole-genome or exome sequencing can measure copy number; fluorescent in situ hybridization (FISH) can localize copies. Clinical interpretation requires consideration of gene content, zygosity, and mosaicism.

In research and medicine, triplications are studied as part of copy-number variation and genome evolution. They illustrate how additional gene dosage can influence phenotype and fitness, and contribute to variation within populations.