FISH vs. CGH — What's the Difference?

FISH (Fluorescence In Situ Hybridization) and CGH (Comparative Genomic Hybridization) are both molecular cytogenetic techniques used to analyze genetic variations and abnormalities. FISH utilizes fluorescent probes that bind to specific DNA sequences on chromosomes, allowing for the visualization of genetic abnormalities, such as deletions, duplications, translocations, and the presence of extra chromosomes. This technique is highly specific and can be used to target specific regions within the genome, making it invaluable in diagnosing genetic diseases, identifying specific pathogens in infections, and in cancer research.

CGH, on the other hand, compares the genomic content of a test sample with a reference sample to identify genomic variations without the need for specific probes. This technique involves labeling test and reference DNA with different fluorescent dyes, co-hybridizing them to a normal metaphase chromosome spread or a microarray, and analyzing the ratio of the fluorescent signals. CGH is particularly useful for detecting unbalanced chromosomal abnormalities across the entire genome, such as gains or losses of chromosome material, but it does not detect balanced rearrangements or the precise location of DNA sequence alterations.

While FISH provides precise localization of genetic changes on chromosomes, CGH offers a broader overview of genomic imbalances between two genomes. FISH's strength lies in its ability to pinpoint specific genetic markers within a complex genome, useful in targeted diagnostics and research. CGH's advantage is its genome-wide screening capability, making it ideal for identifying unknown genetic abnormalities and for comparative genomic studies.

Both FISH and CGH have transformed genetic analysis, each with its unique applications. FISH's ability to visually map the genetic landscape of individual cells offers detailed insights into genetic disorders, while CGH's comparative approach is invaluable in detecting and cataloging genomic variations on a broader scale. Together, these techniques provide powerful tools for understanding the genetic basis of diseases and for developing targeted genetic therapies.

FISH and CGH represent complementary approaches to genetic analysis. FISH is highly specific and localized, ideal for detailed chromosomal examinations, whereas CGH provides a comprehensive view of genomic alterations without the need for prior knowledge of specific genetic targets. The choice between FISH and CGH depends on the research or diagnostic goals, with each method offering distinct benefits in the field of genetic analysis.