By Team Aakash Byju's

Causes of Chromosomal Disorders: Class 12 Biology Notes

Chromosomal Disorders are genetic abnormalities caused by changes in one or more chromosomes. This can be divided into several categories:

Aneuploidy is a situation in which chromosomes are lost or gained as a result of abnormal gene segregation during cell division.

It can result in Monosomy, Trisomy, Tetrasomy and other abnormalities.

Down Syndrome is a kind of trisomy in which there is an extra copy of chromosome 21.

Klinefelter Syndrome is a genetic disorder that occurs in males due to the presence of an extra X chromosome.

Turner Syndrome is a chromosomal disorder caused due to the lack of one X chromosome in females.

Euploidy is a disorder caused by the loss or gain of an entire set of chromosomes, which is most common in plants. It is further subdivided into:

Addition of one or more sets of chromosomes.



Loss of one chromosomal set.

The chromosomal disorders caused by structural abnormalities are further categorized into four groups:


It refers to the existence of an extra portion of a chromosome.


During cell division, a section of a chromosome is lost.


It is the outcome of a chromosomal segment breaking and rejoining after spinning by 180 degrees on its own axis.

 Translocation is the transfer of a section of a chromosome to a non-homologous one.