The right answer is Non-disjunction during meiosis.
Homogeneous aneuploidies, when homogenous, most often result from meiotic non-disjunction and may result in trisomy (presence of a supernumerary normal chromosome) or monosomy (loss of a chromosome). Non-disjunction is defined by the fact that two chromosomes migrate to the same pole during anaphase and pass together in the same daughter cell, instead of migrating each to a daughter cell. This nondisjunction can occur during a maternal or paternal meiotic division. It can involve two homologous chromosomes, during the first meiotic division, or two sister chromatids, during the second meiotic division.
