How can crossing over lead to non-disjunction?

Crossing over is the exchange of genetic material between homologous chromosomes during meiOSis, which can create new allele combinations. If crossing over occurs incorrectly, it may result in chromosomes that are unevenly distributed during cell division. This improper distribution can lead to non-disjunction, where homologous chromosomes or sister chromatids fail to separate, resulting in gametes with an abnormal number of chromosomes. Thus, errors in crossing over can indirectly contribute to the occurrence of non-disjunction.