Aneuploidy is a chromosomal aberration or genomic mutation in which there is an abnormal number of chromosomes in a cell. For example:

Autosomal aneuploidy

• Patau’s syndrome – trisomy of chromosome 13.
• Edwards syndrome – trisomy of chromosome 18.
• Down syndrome – trisomy of chromosome 21.

Gonosomal aneuploidy

• Turner syndrome – a condition where an individual has only an X gonosome, gonosomal aneuploidy.
• Klinefelter’s syndrome – gonosomes are complemented by a second X chromosome – XXY.

Chromosomal mosaics

• Mosaic Turner syndrome