Non-disjunction

• Non-disjunction refers to the chromosomes failing to separate correctly, resulting in gametes with one extra, or one missing, chromosome (aneuploidy)

The failure of chromosomes to separate may occur via:

• Failure of homologues to separate in Anaphase I (resulting in four affected daughter cells)
• Failure of sister chromatids to separate in Anaphase II (resulting in only two daughter cells being affected)