meiotic nondisjunction

genetics

Written by

The Information Architects of Encyclopaedia Britannica

Last updated

July 16, 2026

Quick Summary

Meiotic nondisjunction is the failure of chromosomes or sister chromatids to separate properly during meiosis, a type of cell division that produces gametes (sex cells). This process normally results in four genetically distinct haploid cells, each with half the number of chromosomes of the original diploid cell.12

When nondisjunction occurs, it leads to daughter cells with an incorrect number of chromosomes. This can result in gametes with either too many or too few chromosomes. These numerical abnormalities in chromosomes are believed to generally stem from meiotic nondisjunction and can lead to genetic diseases. For example, Down syndrome is associated with trisomy 21, meaning an extra copy of chromosome 21 is present. Maternal age is a significant factor, with older women having a higher risk of conceiving a child with a chromosomal abnormality.3

Summary created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

4 Britannica Sources

Ask Britannica AI about this topic

Britannica doesn't have a full article on this topic, so we've curated a list of our relevant coverage.

autosome
…generally thought to result from meiotic nondisjunction—that is, the unequal division of chromosomes between daughter cells—that can occur during either maternal or paternal gamete formation. Meiotic nondisjunction leads to eggs or sperm with additional or missing chromosomes. Down syndrome is probably the best-known and most commonly observed of the autosomal…
Read More
…generally thought to result from meiotic nondisjunction—that is, the unequal division of chromosomes between daughter cells—that can occur during either maternal or paternal gamete formation. Meiotic nondisjunction leads to eggs or sperm with additional or missing chromosomes. Down syndrome is probably the best-known and most commonly observed of the autosomal…
Read More

human genetic disease
Numerical abnormalities
…believed generally to result from meiotic nondisjunction—that is, the unequal division of chromosomes between daughter cells—that can occur during either maternal or paternal gamete formation. Meiotic nondisjunction leads to eggs or sperm with additional or missing chromosomes. Although the biochemical basis of numerical chromosome abnormalities remains unknown, maternal age clearly…
Read More
…believed generally to result from meiotic nondisjunction—that is, the unequal division of chromosomes between daughter cells—that can occur during either maternal or paternal gamete formation. Meiotic nondisjunction leads to eggs or sperm with additional or missing chromosomes. Although the biochemical basis of numerical chromosome abnormalities remains unknown, maternal age clearly…
Read More