Comparative genomic hybridization

Comparative Genomic Hybridization (CGH) is a molecular cytogenetic method for analyzing copy number variations (CNVs) in the DNA content of a cell's genome. CGH is widely used in genetic research and diagnostics to detect and map the presence of DNA segments that are gained or lost across the genome. This technique is particularly valuable in the study of cancer genetics, where it helps in identifying genetic alterations that may lead to tumorigenesis.

Overview

Comparative Genomic Hybridization involves comparing the DNA of a test sample with a reference sample to identify variations in genomic content. The process begins with the extraction of DNA from both the test and reference samples. The DNA from each sample is then labeled with different fluorescent dyes. The labeled DNAs are co-hybridized onto a DNA microarray or a metaphase chromosome spread. Following hybridization, the array or chromosomes are analyzed under a fluorescence microscope. The ratio of the fluorescence intensities reflects the relative abundance of DNA sequences in the test sample compared to the reference sample. An increase in the ratio indicates a gain of genetic material in the test sample, while a decrease suggests a loss.

Applications

CGH has a wide range of applications in medical genetics and cancer research. It is used to:

• Detect Genomic Imbalances in various genetic disorders.
• Identify Chromosomal Abnormalities in prenatal and postnatal diagnostics.
• Characterize Oncogenes and Tumor Suppressor Genes in cancer.
• Guide targeted therapy by identifying genetic alterations in tumors.

Advantages and Limitations

The main advantage of CGH is its ability to scan the entire genome for CNVs without prior knowledge of specific regions of interest. However, CGH has limitations, including its inability to detect balanced chromosomal rearrangements, such as translocations and inversions, and its lower resolution compared to other genomic techniques like next-generation sequencing.

Recent Developments

Recent advancements in CGH technology have led to the development of array-based Comparative Genomic Hybridization (aCGH). aCGH offers higher resolution and throughput compared to traditional CGH, enabling more detailed genomic analysis. This has significantly improved the detection of small CNVs and has expanded the utility of CGH in clinical diagnostics and research.

Conclusion

Comparative Genomic Hybridization is a powerful tool for the analysis of genomic copy number variations. Despite its limitations, CGH continues to play a crucial role in the fields of genetics and oncology, providing insights into the molecular mechanisms of diseases and guiding therapeutic strategies.