DNA & Disease Association

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We have already studied structure of DNA in earlier lectures. DNA is selected as genetic material by nature due to self replicating property and repair mechanism. There are several experiments which prove that the DNA acts as genetic vehicle for transfer of information from one to next generation.

There is a range of diseases which have certain genetic background (except, diseases caused by microorganisms). Since, DNA is the genetic material and carries all the informations required for the growth and development of an individual, any change in the DNA leads to some abnormality. DNA is present in form of chromosomes inside the nucleus so, the change in DNA can be explained in terms of change in chromosomes or chromosomal aberration.

Chromosomal aberrations:

Any change in normal chromosome of the cell, referred as chromosomal aberration. This may be due to structural or numerical change.

Structural change: Following structural changes can lead to a disease (Fig. 1).

1.  Deletion: This is due to loss of a part of a chromosome.

Wolf-Hirschhorn syndrome : Partial deletion of the short arm of chromosome no. 4.

Jacobsen syndrome : Deletion of terminal part of long arm of chromosome no. 11.

Cri du chat syndrome: Partial deletion of the short arm of chromosome no. 5.

2.  Duplication: This is due to addition or duplication of a part of chromosome.

Bar eye in drosophila: Duplication of 16A region of X chromosome of Drosophila.

Charcot-Marie-Tooth Disease type 1A : Duplication of a large region in chromosome 17p12.

3.  Translocation: This is due to movement of a part of chromosome to other chromosome. It may be reciprocal or robertsonian type.

Leukemia ( acute myelogenous leukemia & chronic myelogenous leukemia ) and Ewing's sarcoma is generally caused by translocation.