The chromosomal abnormality is caused due to abnormal chromosome numbers in cells.
This occurs due to various forms of mutations and improper segregation of chromosomes during cell division.
Example: Down syndrome is an example of aneuploidy.
It is an example of aneuploidy abnormality which is caused due to an extra copy of chromosome 21, thus the affected individual has 47 chromosomes.
The abnormal person is characterized by a round and flat, a small nose with a flat low bridge, the back of the head is slightly flat, and a larger tongue.