Disorders caused by absence, excess or abnormal arrangement of chromosomes are called

1. Genetic disorders fall into two broad groups. 2. Mendelian disorders arise from a change in a single gene. 3. Chromosomal disorders are caused by absence, excess or abnormal arrangement of one or more chromosomes. 4. Down's, Turner's and Klinefelter's syndromes are the common examples. 5. The distinction decides whether a karyotype or a gene test is the right investigation. _Source: syllabus Biology Ch4 'Principles of Inheritance and Variation'_