what is non disjunction

Nondisjunction is a genetic condition that occurs when chromosomes or chromatids fail to separate correctly during cell division. This results in daughter cells with abnormal numbers of chromosomes, which is known as aneuploidy. Nondisjunction can occur during anaphase of mitosis, meiosis I, or meiosis II. There are three forms of nondisjunction: failure of a pair of homologous chromosomes to separate in meiosis I, failure of sister chromatids to separate during meiosis II, and failure of sister chromatids to separate during mitosis. Nondisjunction can cause chromosomal abnormalities such as Down syndrome, Patau’s Syndrome, Edwards Syndrome, Klinefelter Syndrome, and Turner’s Syndrome. Nondisjunction is caused due to inactivation of topoisomerase II, separase or condensin. Nondisjunction can be diagnosed by karyotyping, and amniocentesis is carried out to take out amniotic fluid, which is analyzed and any chromosomal abnormalities in the fetus can be diagnosed.