Chromosomal aberrations, also known as chromosomal abnormalities, are changes to the structure or number of chromosomes, which are strands of condensed genetic material. Humans typically have 23 pairs of chromosomes, of which 22 pairs are autosomal, numbered 1 through 22. The last pair of chromosomes are sex chromosomes, which determine an individual’s sex assignment. Chromosomal aberrations can be caused by errors during cell division, which can occur via mitosis or, only in sex chromosomes, meiosis. There are two main types of chromosomal aberrations:

• Numerical Abnormalities: This occurs when there is an atypical number of chromosomes. For example, Down syndrome is caused by an extra copy of chromosome 21.

• Structural Abnormalities: This occurs when one or more individual chromosomes are altered. Examples of structural abnormalities include deletions, translocations, inversions, duplications, ring chromosomes, and isochromosomes.

Chromosomal aberrations can lead to genetic disorders, such as Down syndrome, and can also be associated with cancer. Chromosome aberrations can be visualized at mitosis when cells divide, and some types of aberrations, such as dicentric chromosomes, can be used as a biological dosimeter to measure exposure to radiation or carcinogens.