Chromosome abnormality

A change in chromosome number or structure that can alter gene dosage, disrupt genes, or affect inheritance and development.

Chromosome: A DNA molecule packaged with proteins that carries genetic information in cells. Chromosome abnormalities alter the number or structure of these genetic packages.
Aneuploidy: A chromosome-number abnormality involving the gain or loss of individual chromosomes. It describes the numerical changes that result when particular chromosomes are missegregated.
Karyotyping: A laboratory method that images and arranges chromosomes to assess their number and structure. It detects many large chromosome abnormalities in cells.
Down syndrome: A genetic condition usually caused by an extra copy of chromosome 21. It is a well-known example of an autosomal chromosome-number abnormality.
Single-nucleotide variant: A genetic variant in which one nucleotide in a DNA sequence differs from the reference sequence. Unlike most chromosome abnormalities, it changes a single DNA position.
Karyotype: The number and visual appearance of chromosomes in a cell or organism. Karyotyping reveals many numerical and large structural abnormalities.
Polyploidy: The presence of more than two complete sets of chromosomes in a cell or organism. It is a numerical abnormality involving whole chromosome sets rather than individual chromosomes.
Fluorescence in situ hybridization: A technique that uses fluorescent DNA probes to locate specific sequences in chromosomes or cells. It can test for targeted chromosome gains, losses, or rearrangements.
Turner syndrome: A condition in females associated with complete or partial absence of one X chromosome. It illustrates how loss of a sex chromosome affects development.
Copy-number variation: A DNA segment that varies in copy number among individuals, sometimes without causing disease. It overlaps with chromosome abnormalities but can describe benign inherited variation.

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