Introduction
Chromosomal aberrations refer to changes in the normal structure or number of chromosomes. These changes can lead to genetic disorders, developmental abnormalities, or even cancer. Chromosomal aberrations may occur due to errors during cell division, exposure to radiation, or chemical mutagens.
Definition
A chromosomal aberration is any change in the number or structure of chromosomes that results in genetic imbalance or abnormalities in an organism.
Types of Chromosomal Aberrations
I. Structural Chromosomal Aberrations
These involve changes in the structure of a chromosome due to breakage and incorrect rejoining.
1. Deletion
A segment of the chromosome is lost or deleted. It can be terminal (end) or interstitial (middle).
Example: Cri-du-chat syndrome (deletion on chromosome 5)
2. Duplication
A portion of the chromosome is duplicated, resulting in extra genetic material.
Example: Charcot-Marie-Tooth disease (duplication on chromosome 17)
3. Inversion
A segment of a chromosome is reversed end to end. It may be:
- Paracentric: Does not include the centromere
- Pericentric: Includes the centromere
4. Translocation
A segment from one chromosome is transferred to another. Types include:
- Reciprocal translocation: Exchange between two non-homologous chromosomes
- Robertsonian translocation: Fusion of two acrocentric chromosomes
Example: Some forms of Down syndrome (translocation type)
II. Numerical Chromosomal Aberrations (Aneuploidy)
These involve an abnormal number of chromosomes.
1. Monosomy
One chromosome from a pair is missing (2n – 1).
Example: Turner Syndrome (XO)
2. Trisomy
One extra chromosome is present (2n + 1).
Examples:
- Down syndrome (Trisomy 21)
- Edwards syndrome (Trisomy 18)
- Patau syndrome (Trisomy 13)
3. Polyploidy
Presence of more than two complete sets of chromosomes. Common in plants, rare in humans.
Causes of Chromosomal Aberrations
- Errors in meiosis or mitosis
- Radiation exposure
- Chemicals or drugs
- Viral infections
Detection Methods
- Karyotyping
- FISH (Fluorescence In Situ Hybridization)
- Microarray analysis
Conclusion
Chromosomal aberrations can significantly impact health and development. Understanding these changes helps in diagnosing genetic diseases, guiding treatment, and offering genetic counseling. Advanced diagnostic tools have improved early detection and management of these conditions.