Kopioluku

Kopioluku is a term used in genetics and genomics to denote the number of copies of a specific DNA sequence or genomic locus within a cell or genome. In a typical human diploid cell, most loci have two copies—one on each homologous chromosome. Deviations from this baseline are described as copy-number variations (CNVs), which include deletions (loss of copies) and duplications or amplifications (gain of copies). Copy number can vary between individuals (germline CNVs) and can also differ among cells within a tissue (somatic CNVs), contributing to mosaicism and phenotypic diversity.

Several technologies are used to measure copy number. Array comparative genomic hybridization (array CGH) and SNP genotyping arrays estimate copy number across the genome. Quantitative PCR and digital PCR provide targeted copy-number assays. Sequencing-based methods infer copy number from read depth or allele balance in whole-genome, exome, or targeted sequencing data.

Biological and clinical significance stems from gene dosage effects: increases can raise gene expression and potentially drive disease, for example through oncogene amplification, while deletions can reduce function or reveal recessive defects. Pathogenic CNVs are associated with developmental disorders, neuropsychiatric conditions, and cancer. In research, copy number is an important parameter in studies of genome structure, evolution, and cancer genomics.

Challenges include technical bias, tumor purity and ploidy in cancer samples, mosaicism, and complexities in repetitive genomic regions that impede accurate copy-number calling. See also: copy-number variation, gene dosage, aneuploidy.