Alternative mechanisms of non-disjunction that lead to trisomy

Non-disjunction may occur either during Meiosis I (left) or Meiosis II (right). Note that non-disjunction during Meiosis I means that all products are trisomic or nullisomic, whereas an event in Meiosis II does produce standard products.

Figure ©2002 by Griffiths et al.; all text material ©2014 by Steven M. Carr