Nondisjunction

In biology, nondisjunction is the failure of a chromosome to split correctly during meiosis.

This results in the production of gametes which have either more or less of the usual amount of genetic material, and is a common mechanism for trisomy or monosomy.

Nondisjunction can occur in the meiosis I or meiosis II phases of cellular reproduction.

This is a cause of several medical conditions, including:

• Down Syndrome – trisomy of chromosome 21
• Patau Syndrome – trisomy of chromosome 13
• Edward Syndrome – trisomy of chromosome 18
• Turner Syndrome – only one X chromosome present