What are the mechanisms by which aneuploidy and polyploidy are caused? what are the mechanisms by which aneuploidy and polyploidy are caused? the principal cause of aneuploidy is chromosome nondisjunction during mitosis or meiosis. polyploidy in nature can result either from the duplication of euploid chromosome sets from a single species or from the combining of chromosome sets from different species. the principal cause of aneuploidy is paternal chromosome nondisjunction during meiosis. polyploidy in nature results from the combining of chromosome sets from different species. the principal cause of aneuploidy is chromosome nondisjunction during mitosis. polyploidy in nature can result from the deletion of one chromosome set during meiosis or during the first mitotic division. the principal cause of aneuploidy is maternal chromosome nondisjunction during meiosis. polyploidy in nature results from the deletion of one chromosome set in somatic cells.