Condition of having an abnormal number of certain chromosomes. Aneuploid offspring may result if a normal gamete unites with an aberrant one produced as a result of nondisjunction. An aneuploid cell that has a chromosome in triplicate is said to be trisomic for that chromosome. An aneuploid with a missing chromosome is said to be monosomic for that chromosome. When an aneuploid zygote divides by mitosis, it transmits the chromosomal anomaly to all subsequent embryonic cells.
Some aneuploidies cause characteristic symptoms in survivors.
An example is Down's syndrome which results from trisomy of chromosome 21.