Answer: Aneuploidy occurs during meiosis, in which chromosomes sometimes fail to divide properly; as a result, the person may have 45 or 47 chromosomes.
Explanation: In Aneuploidy, abnormal chromosome number is not an exact multiple of haploid. That is, there might be one chromosome left (45) or one chromosome more (47) than normal (46).
Aneuploidy results from non-disjunction during gametogenesis. The homologous chromosome fail to separate during mitosis or meiosis. Therefore, one daughter cell receives an extra chromosome while the other daughter cell is deficient of one. Following fertilization, the resulting zygote will have either one homologous chromosome (monosomy) or three homologous chromosomes (trisomy).
