Chromosomal Aberrations

 

Chromosomal aberrations are changes in the normal structure or number of chromosomes. These changes can lead to genetic disorders and abnormalities. Chromosomal aberrations are of following types: 

1. Structural Changes

•       Deletion
•       Duplication
•       Inversion
•       Translocation

2. Numerical Changes

•            Aneuploidy
•            Polyploidy

 

 Each type is explained with an example for better understanding.

 

1. Deletion:   Deletion is a type of chromosomal abnormality where a segment of chromosome is missing or "deleted." This can lead to the loss of genes within that segment, often causing serious genetic disorders.

Example: Cri-du-chat Syndrome is caused by the deletion of a part of chromosome number 5. This type of chromosomal aberration results in developmental delays, intellectual disabilities and a characteristic high-pitched cry in infants, which resembles the sound of a cat (hence the name "cri-du-chat").

 

Effects:

Individuals with deletions may exhibit a wide range of symptoms depending on the size of the deletion and the genes affected.

Deletions can cause physical malformations, intellectual disabilities, or severe health issues.

 

2. Duplication: This types of chromosomal aberration occurs when a portion of the chromosome is duplicated, resulting in extra copies of certain genes. This can disrupt normal gene function by increasing the gene dosage.

Example:

Charcot-Marie-Tooth Disease: A duplication of part of chromosome 17 causes this disorder, which affects the peripheral nerves, leading to muscle weakness and atrophy, particularly in the legs and feet.

Effects:

a)      Duplications can cause developmental problems, depending on the size and location of the duplicated segment.

b)      They may lead to conditions such as intellectual disabilities, physical deformities, and other health issues.

 

 3. Inversion: An inversion occurs when a chromosome segment breaks off, rotates 180 degrees, and reattaches to the same chromosome. This does not involve the loss or gain of genetic material but changes the order of the genes.

Example:

Pericentric Inversion: Inversion can be pericentric (involving the centromere) or paracentric (not involving the centromere). One common inversion in humans is Inversion 9 (inv9), which is usually harmless but can sometimes be associated with infertility or miscarriages.

 

Effects:

Inversions typically do not cause abnormalities in the carriers but can lead to problems during reproduction, such as miscarriages or chromosomal abnormalities in offspring.

4. Translocation

A translocation occurs when a segment of one chromosome breaks off and attaches to a non-homologous chromosome. This can be balanced (no genetic material lost) or unbalanced (with extra or missing genetic material).

 

Example:

Chronic Myeloid Leukemia (CML): In this cancer, a segment of chromosome 9 is translocated to chromosome 22, creating the Philadelphia chromosome. This translocation leads to uncontrolled cell division and is a major cause of CML.

 

Effects:

a.       Balanced translocations may not cause any problems for the carrier but can result in unbalanced gametes, leading to miscarriage, infertility, or genetic disorders in offspring.

b.      Unbalanced translocations can lead to developmental disorders and congenital malformations.