Genes are not the only things that change. Chromosomal mutations alter the structure or number of entire chromosomes and often affect many genes at once. These changes can arise during DNA replication, repair, or chromosome segregation.

Structural mutations include deletions, duplications, inversions, and translocations. Numerical mutations produce aneuploidy. Large deletions or duplications frequently cause developmental syndromes because gene dosage is disrupted. Balanced translocations may have no immediate effect on the carrier yet lead to unbalanced gametes.

Cytogenetic techniques such as karyotyping and chromosomal microarray detect these rearrangements. Some chromosomal mutations are compatible with life; others result in miscarriage or severe disability. Studying them reveals critical genomic regions and informs prenatal diagnosis.

• Change in chromosome structure or number
• Includes deletions, duplications, and aneuploidy
• Often affects multiple genes
• Detected by cytogenetic methods