What is a nondisjunction? hints what is a nondisjunction? an error in which a diploid cell or organism has an extra chromosome of one type, producing a chromosome number of 2n + 1 an error in cell division that causes homologous chromosomes or sister chromatids to move to the same side of the dividing cell an error in which a diploid cell or organism lacks a chromosome of one type, producing a chromosome number of 2n - 1 none of the above?