Nondisjunction, also known as mosaicism, chromosomal, is related to down syndrome and trisomy x. An important gene associated with Nondisjunction is MTHFR (Methylenetetrahydrofolate Reductase), and among its related pathways/superpathways are Methotrexate Pathway (Cancer Cell), Pharmacodynamics and Pharmacokinetics and MTHFR deficiency. Affiliated tissues include bone marrow and testes, and related phenotypes are decreased fertility and abnormality of chromosome segregation