1.5.9 Copy Number Alteration Definition

Copy Number Alteration Definition is the description of a genetic change in which a cell possesses an abnormal number of copies of a particular segment of DNA, whether an individual gene, a larger genomic region, or an entire chromosome, differing from the number of copies normally present in a healthy cell. Rather than altering the sequence of the DNA itself, a copy number alteration changes how many times a given piece of genetic material is repeated within the genome, affecting the overall dosage of any genes located within the altered region.

Forms of Copy Number Alteration

Amplification

An amplification refers to an increase in the number of copies of a particular genomic region beyond the normal count, resulting in extra copies of any genes located within that region and, typically, a corresponding increase in the amount of the associated gene products produced.

Deletion of Genomic Copies

A copy number alteration can also take the form of a reduction in the number of copies of a genomic region below the normal count, including the complete loss of both copies in some cases, reducing or eliminating the dosage of any genes located within the affected region.

Mechanisms Producing Copy Number Alteration

Errors During Cell Division

Copy number alterations can arise from errors occurring during the process by which a cell's chromosomes are copied and distributed to daughter cells, resulting in offspring cells that inherit an incorrect number of copies of particular genomic regions.

Structural Genomic Rearrangement

Copy number alterations can also result from structural rearrangement processes that duplicate or eliminate specific segments of DNA, producing localized changes in copy number without necessarily affecting an entire chromosome.

Functional Consequences of Altered Copy Number

Dosage Effects on Gene Activity

Because the overall amount of a gene's product is often influenced by how many copies of that gene are present, copy number alterations can meaningfully change a cell's level of gene activity even without any change to the underlying DNA sequence itself.

Amplification of Growth-Promoting Genes

When a copy number alteration increases the number of copies of a gene that promotes proliferation, the resulting increase in gene dosage can drive excessive activity of that growth-promoting pathway, contributing to a proliferative advantage.

Loss of Growth-Restraining Genes

When a copy number alteration reduces or eliminates the copies of a gene that normally restrains growth, the corresponding reduction in that gene's protective activity can remove an important barrier to uncontrolled proliferation.

Relevance to Cancer Cell Biology

Copy number alterations represent a distinct and clinically important category of genetic change in cancer, capable of significantly influencing gene activity through changes in dosage rather than sequence, and their assessment provides essential complementary information alongside sequence-level alterations such as single nucleotide variants, insertions, and deletions when characterizing the full genetic landscape of a cancer cell.