4.  Inversion: This is due to reverse orientation of a part of chromosome. It may be paracentric (centromere is not included) or pericentric (centromere is included).

Figure 1: Possible structural changes in chromosomes.

Numerical change: Numerical changes in chromosome can also lead to a diseased condition. The numerical changes are mainly of two types.

A. Aneuploidy: Change (increase or decrease) of one or two chromosome from a chromosome pair.

Monosomy (2n-1): Turner syndrome (XO): Loss of one X chromosome.

Nullisomy (2n-2): Loss of one complete set of chromosome (patient will not survive).

Trisomy (2n+1): Down syndrome or Mongolism: Trisomy of 21 st pair of chromosome.

Edwards syndrome: Trisomy of 18 th pair of chromosome.

Patau syndrome: Trisomy of 13 st pair of chromosome.

Klinefelter syndrome (47,XXY) : Extra X chromosome in male sex chromosome set.