The symptoms of a genetic order are short-statured with a small round head furrowed tongue and partially open mouth. Such a genetic disorder is characterized by the presence of an extra chromosome number ______.   

Down’s syndrome results in the gain of extra copy of chromosome 21. The affected individual is short statured with small round head, furrowed tongue and partially open mouth. Palm is broad with characteristic palm crease. Physical, psychomotor and mental development is retarded.