the correct answer would be nondisjunction.
nondisjunction refers to the failure or improper division of chromosomes during a cell division.
it can occur in meiosis i, meiosis ii as well as in mitosis.
in anaphase i of meiosis i nondisjunction results in improper segregation of homologous chromosomes due to which one cell gets two copies of the chromosome and other cell does not get a single copy of that chromosome.
similarly, in anaphase ii, the sister chromatids are improperly divided due to nondisjunction. it results in a situation in which one daughter cell posses an extra copy of the chromosome while the daughter cell lacks that chromosome.
for example, in down syndrome trisomy of chromosome 21 occurs due to nondisjunction.
it has all membrane bound organelles