NCI Dictionary of Genetics Terms

The NCI Dictionary of Genetics Terms contains technical definitions for more than 200 terms related to genetics. These definitions were developed by the PDQ® Cancer Genetics Editorial Board to support the evidence-based, peer-reviewed PDQ cancer genetics information summaries.

chromosomal instability
(KROH-muh-SOH-mul IN-stuh-BIH-lih-tee)
A genomic imbalance that occurs when a cell has an abnormal number of chromosomes. This can be caused by unexpected chromosomal crossover or by the presence of small, extra-chromosomal pieces of DNA.