What is the Difference Between CGH and Array CGH

The key difference between CGH and array CGH is that CGH is a traditional molecular cytogenetic method for analyzing copy number variation in DNA of a test sample that has a lower resolution, while array CGH is a fully automated molecular cytogenetic method for analyzing copy number variation in DNA of a test sample that has a higher resolution.

CGH and array CGH are two techniques to detect copy number variations in individuals. Copy number variation refers to the sections of the genome that are repeated. Copy number varies between individuals. Copy number variation is generally categorized into two groups: short repeats and long repeats. One of the most well-known examples for a short copy number variation is the repeat of the CAG trinucleotide in the huntingtin gene. This causes a neurological disorder called huntingtin. The best example for long repeats copy number variation is the alpha amylase gene, which causes insulin resistance. Copy number variation can be detected by techniques such as FISH, CGH, and array CGH.

CONTENTS

1. Overview and Key Difference
2. What is CGH 
3. What is Array CGH
4. Similarities – CGH and Array CGH
5. CGH vs Array CGH in Tabular Form
6. Summary – CGH vs Array CGH

What is CGH?

CGH is a traditional molecular cytogenetic method for analyzing copy number variation in DNA of a test sample compared to a reference sample. It has a lower resolution compared to automated techniques. The objective of this technique is to quickly and efficiently compare two genomic DNA samples that arise from different sources.

The procedure involves the isolation of DNA from two sources: test and reference. Then the next step is independent labelling of test and reference DNA samples with fluorophores of different colours. Later, the two DNA samples were denatured in order to get the single-stranded DNA samples. Finally, the hybridization of the two resultant DNA samples in a 1:1 ratio to a normal metaphase spread of chromosomes was performed. The chromosomal differences can be identified between the two sources using a fluorescence microscope and computer software. Furthermore, the CGH technique is only able to detect unbalanced chromosomal abnormalities.

What is Array CGH?

Array CGH is a fully automated molecular cytogenetic method for analyzing copy number variation in the DNA of a test sample compared to a reference sample. It has a higher resolution, and it was developed in order to minimize the limitations of traditional CGH. Array CGH combines the principles of CGH with the use of microarrays. Instead of using metaphase chromosomes spread, this method uses slides arrayed with small segments of DNA as the targets. These microarrays were made by depositing and immobilizing a small amount of DNA (probes) on a solid glass support. The size of probes can vary from oligonucleotide to a bacterial artificial chromosome.

Regardless of probes, the basic method of array CGH is similar to CGH. Once probes containing microarray are prepared, the two DNA samples (test and reference) labelled with fluorophores of different colours are mixed together and added to the microarray. Since the DNA in the samples is single-stranded due to denaturation, this DNA hybridize with arrayed single-stranded probes. Using a digital imaging system, it is possible to identify the chromosomal differences between the two sources.

What are the Similarities Between CGH and Array CGH?

• CGH and array CGH are two techniques to detect copy number variations.
• They are molecular cytogenetic methods.
• Both methods diagnose unbalanced chromosomal abnormalities.
• Fluorophores are involved in both methods.
• Both methods can be used to detect genetic disorders due to copy number variations.
• They are widely used in comparative genomic analysis.

What is the Difference Between CGH and Array CGH?

CGH is a traditional molecular cytogenetic method for analyzing copy number variation in DNA of a test sample that has a lower resolution, while array CGH is a fully automated molecular cytogenetic method for analyzing copy number variation in DNA of a test sample that has a higher resolution. So, this is the key difference between CGH and array CGH. Furthermore, in CGH, test and reference DNA samples hybridize with a normal metaphase spread of chromosomes, but in array CGH, test and reference DNA samples hybridize with the immobilized DNA probes containing microarray.

The below infographic lists the differences between CGH and array CGH in tabular form for side by side comparison.

Summary – CGH vs Array CGH

CGH and array CGH are two molecular cytogenetic techniques to detect unbalanced chromosomal abnormalities. They are widely used in comparative genomic analysis. CGH is a traditional molecular cytogenetic method for analyzing copy number variation in DNA of a test sample that has a lower resolution. In contrast, array CGH is a fully automated molecular cytogenetic method for analyzing copy number variation in DNA of a test sample that has a higher resolution. Thus, this summarizes the difference between CGH and array CGH.

Reference:

1. “Comparative Genomic Hybridization.” An Overview | ScienceDirect Topics.
2. Heather, James M., and Benjamin Chain. “The Sequence of Sequencers: The History of Sequencing DNA.” Genomics, Academic Press, 10 Nov. 2015.

Image Courtesy:

1. “CGH schema” By Mbaudis (talk) (Uploads) – Own work (CC BY 2.5) via Commons Wikimedia
2. “Array-CGH protocol” By Philippe Hupé – Emmanuel Barillot, Laurence Calzone, Philippe Hupé, Jean-Philippe Vert, Andrei Zinovyev,Computational Systems Biology of Cancer Chapman &  “Hall/CRC Mathematical” Computational Biology , 2012 (CC BY-SA 3.0) via Commons Wikimedia