Written by the Fiveable Content Team • Last updated September 2025
Verified for the 2026 exam
Verified for the 2026 exam•Written by the Fiveable Content Team • Last updated September 2025
Definition
Down Syndrome is a genetic disorder caused when abnormal cell division results in an extra full or partial copy of chromosome 21.
Related terms
Trisomy: A condition in which an organism has three copies of a particular chromosome instead of the usual two.
Chromosome 21: The smallest human autosome with about 48 million base pairs, it is estimated to carry between 200 and 400 genes. An extra copy results in Down Syndrome.
Genetic Disorder: A disease caused by abnormalities in an individual's genome, such as Down Syndrome.