Aneuploidy

Aneuploidy is a chromosome-number state in which a cell has gained or lost one or more individual chromosomes, rather than entire chromosome sets.

Nondisjunction: The failure of homologous chromosomes or sister chromatids to separate properly during cell division. This segregation error produces daughter cells with unequal chromosome counts.
Gene dosage: The number of copies of a gene available to produce RNA or protein. Gaining or losing a chromosome changes the dosage of many genes at once.
Edwards syndrome: A genetic condition caused by an extra copy of chromosome 18, usually present in all or some cells. Trisomy 18 is a severe example of autosomal aneuploidy.
Theodor Boveri: A German biologist whose experiments linked abnormal chromosome complements with abnormal development. His sea-urchin studies helped establish the biological significance of chromosome number.
Cancer: A group of diseases in which abnormal cells grow and spread without normal control. Aneuploidy is common in many cancers, but its role in tumor development varies.
Mitotic checkpoint: A cell-cycle control system that delays chromosome separation until chromosomes are properly attached to the spindle. Checkpoint failure can let chromosome-segregation errors create aneuploid cells.
Down syndrome: A genetic condition usually caused by an extra copy of chromosome 21. It is a common viable example of autosomal aneuploidy.
Patau syndrome: A genetic condition caused by an extra copy of chromosome 13, usually present in all or some cells. Trisomy 13 shows the consequences of an additional autosome.
Walter Sutton: An American geneticist who connected chromosome behavior during meiosis with Mendel's laws of inheritance. Chromosome theory clarified how segregation errors could alter chromosome counts.
Tumor heterogeneity: The coexistence of genetically or behaviorally distinct cancer-cell populations within a tumor. Ongoing chromosome gains and losses can diversify tumor cell populations.

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