Color enhanced Transmission Electron Micrograph (TEM) showing radiation damage to chromosomes. A chromosome abnormality, disorder, anomaly, aberration, or mutation is a missing, extra, or irregular portion of chromosomal DNA. When cells are exposed to radiation or carcinogens, DNA sometimes breaks, and the broken ends may rejoin in different patterns from their original arrangement. The abnormalities that result are termed chromosome aberrations and may be visualized at mitosis when cells divide. Magnification: unknown.