What are chromosome abnormalities?

Chromosome abnormalities usually occur due to a mistake during cell division. There are many types of errors that can occur resulting in several different types of chromosome abnormalities that can take place. All of these chromosomal abnormalities can be categorized into two basic groups - numerical abnormalities and structural abnormalities.

Numerical Abnormalities result when an individual is either missing one of the chromosomes from the pair or they have more than two chromosomes instead of a pair. 

• When an individual has less than a pair of chromosomes, the condition is known as monosomy. 
• When an individual has one more than a pair of chromosomes, the condition is known as trisomy.

Structural abnormalities result when the structure of the chromosome is altered. This may happen in one of several ways. 

• Duplications occur when a portion of a chromosome is duplicated, resulting in extra genetic material. 
• Deletions result when a portion of a chromosome is deleted or missing. 
• Inversions occur when a portion of a chromosome breaks off, gets turned upside down, and reattaches itself, resulting in the genetic material getting inverted.
• Translocations result when a portion of one chromosome is transferred to another chromosome. 
• Rings are a type of chromosomal abnormality that result from a portion of a chromosome breaking off and forming a circle or ring. In this case, there may or may not be a loss of genetic material.