The full form of CGH is Comparative Genomic Hybridization.
What is Comparative Genomic Hybridization (CGH)?
Comparative Genomic Hybridization (CGH) is a molecular cytogenetic technique used to detect copy number variations (CNVs) in DNA. CNVs are changes in the number of copies of specific DNA segments, which can be either gains (duplications) or losses (deletions) of genetic material.
How does CGH work?
CGH works by comparing the DNA from a test sample (e.g., a tumor cell) to a reference DNA sample (e.g., normal cells). Both DNA samples are labeled with different fluorescent dyes and then hybridized to a microarray containing DNA fragments representing the entire genome.
- If the test DNA has a higher copy number of a particular gene or region, the corresponding spot on the microarray will fluoresce more brightly with the test DNA dye.
- Conversely, if the test DNA has a lower copy number, the spot will fluoresce more brightly with the reference DNA dye.
By analyzing the fluorescence ratios across the microarray, researchers can identify regions of the genome where the test DNA has gained or lost copies of genes.
Applications of CGH:
CGH is widely used in various fields, including:
- Cancer research: Detecting chromosomal abnormalities in cancer cells to identify potential targets for therapy.
- Genetic diagnosis: Diagnosing genetic disorders associated with CNVs, such as autism spectrum disorder, intellectual disability, and developmental delay.
- Prenatal screening: Detecting CNVs in fetal DNA to identify potential risks for genetic disorders.
- Evolutionary studies: Studying the evolution of genomes by comparing the CNV profiles of different species.
Types of CGH:
There are two main types of CGH:
- Array CGH (aCGH): Uses a microarray with thousands or millions of DNA probes representing specific genomic regions.
- Chromosomal CGH (cCGH): Uses metaphase chromosomes as probes.
Advantages of CGH:
- High sensitivity: Can detect small changes in copy number.
- Genome-wide coverage: Can analyze the entire genome simultaneously.
- Relatively simple and cost-effective: Compared to other molecular cytogenetic techniques.
Limitations of CGH:
- Limited resolution: Cannot detect small CNVs or single-nucleotide polymorphisms (SNPs).
- Not suitable for detecting balanced chromosomal rearrangements: Such as translocations or inversions.
