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Comparative Genomic Hybridization

Infer relative genomic copy-number gains and losses by competitively hybridizing differently labeled test and reference DNA and mapping their normalized signal ratio by locus.

Version
v2 · 2026-09-19 · History
Domain-specific #
1512
Domain group
Natural Sciences
Origin domain
Biology & Ecology
Subdomains
Cytogenetics, Genome Wide Copy Number Analysis → Biology & Ecology
Aliases
CGH, Chromosomal CGH, Comparative genome hybridization

Core Idea

Comparative genomic hybridization (CGH) is a molecular-cytogenetic measurement architecture for detecting relative DNA copy-number gains and losses across a genome. Genomic DNA from a test sample and a reference sample is labeled with distinguishable fluorophores, mixed, and competitively hybridized to a common locus-ordered substrate. The normalized test-to-reference signal ratio is mapped by genomic position; departures from the balanced ratio indicate relative dosage differences.

Conventional CGH uses normal metaphase chromosomes as the substrate. Array CGH replaces chromosomes with mapped DNA probes, raising and regularizing resolution while retaining the same comparative-ratio principle.

How would you explain it like I'm…

Two-Color DNA Comparison

Inside every cell is a long instruction book called DNA. Scientists take DNA from a sample they want to check and color it green, and DNA from a normal sample and color it red. They mix them and let both stick to the same map. Where the sample has extra copies of some pages, that spot looks greener; where it's missing pages, it looks redder. That's comparative genomic hybridization.

Finding Extra or Missing DNA

Comparative genomic hybridization, or CGH, is a lab method that finds places where a sample's DNA has too many or too few copies of a stretch. Scientists take DNA from the sample being tested and from a normal reference, and tag each with a different glowing color. They mix the two and let them stick to the same guide, which is laid out in order along the chromosomes. At each spot they compare how much of each color stuck. If the colors are balanced, the copy number matches; if one color wins, the sample has gained or lost DNA there. It can't find every kind of DNA change, only these extra or missing amounts.

Two-Color Copy-Number Comparison

Comparative genomic hybridization (CGH) is a method for finding gains and losses of DNA copy number across a whole genome. DNA from a test sample and from a reference sample is labeled with two different fluorescent dyes, mixed, and allowed to compete for binding (hybridization) to the same ordered targets. At each position in the genome, scientists measure the ratio of test to reference signal; a balanced ratio means equal copies, while a higher or lower ratio means relative gain or loss. Traditional CGH uses normal chromosomes as the targets, while array CGH uses many mapped DNA probes, giving finer and more even resolution. CGH detects imbalances in copy number, not every type of genetic change — for example, a balanced rearrangement doesn't change the ratio.

 

Comparative genomic hybridization (CGH) is a molecular-cytogenetic measurement architecture for detecting relative DNA copy-number gains and losses genome-wide. Test and reference genomic DNA are labeled with distinguishable fluorophores, mixed, and competitively hybridized to a common locus-ordered substrate; the normalised test-to-reference fluorescence ratio is then mapped by genomic position, and departures from the balanced ratio indicate relative dosage differences. Conventional CGH uses normal metaphase chromosomes as the substrate; array CGH substitutes mapped DNA probes, increasing and regularising resolution while keeping the same comparative-ratio principle. The analysis pipeline includes normalisation of signal ratios and segmentation of the ratio profile into regions of gain, loss or balance before copy-number interpretation. Because the readout is relative dosage, CGH detects imbalances but not copy-neutral changes such as balanced rearrangements, and results are relative to the chosen reference.

Scope of Application

CGH recurs in cancer cytogenetics, tumor evolution, constitutional copy-number analysis, developmental-disorder investigation, prenatal or postnatal diagnostics, model-organism genomics, and research screening for deletions and amplifications.

Conventional chromosomal CGH and array CGH are variants of the same abstraction. Their substrates, resolution, dynamic range, DNA requirements, and processing differ, but each compares two genomic samples by competitive hybridization and spatial signal ratio.

Clinical use requires validated platforms, quality controls, reference populations, interpretation standards, and confirmatory or orthogonal tests where appropriate. This node describes the measurement architecture, not a stand-alone medical recommendation.

Clarity

Recognition begins with two genomic DNA inputs and different labels. If a single sample is hybridized without a comparative reference signal, the assay is not CGH in this exact sense. Both samples must address the same ordered loci under comparable conditions.

For locus \(i\), a common summary is

Manages Complexity

CGH converts millions or billions of genomic bases into a spatial dosage profile. Instead of selecting one suspected locus at a time, it surveys the genome and routes anomalous regions to focused interpretation.

Competitive co-hybridization controls many environmental variables because test and reference experience the same substrate and reaction. Taking their ratio cancels shared multiplicative effects more effectively than comparing unrelated absolute signals.

Abstract Reasoning

Let true hybridizable copy amounts at locus \(i\) be \(C_{T,i}\) and \(C_{R,i}\). A simplified model is

\[ I_{T,i}=a_T h_i C_{T,i}+\epsilon_{T,i},\qquad I_{R,i}=a_R h_i C_{R,i}+\epsilon_{R,i}, \]

where \(h_i\) represents locus-specific hybridization efficiency and \(a_T,a_R\) label/channel effects. After normalization, the ratio reduces the shared \(h_i\) and estimates \(C_{T,i}/C_{R,i}\).

Knowledge Transfer

Literal transfer holds across chromosomal and array platforms because test/reference competition and locus-resolved ratio remain invariant. Cancer, prenatal, and constitutional contexts change samples and interpretation, not the comparator architecture.

The portable residue is ratio-based comparative measurement: expose target and reference to shared conditions and infer relative quantity from their signal quotient. Live Ratio supplies this core. CGH adds genomic DNA, hybridization, fluorophores, ordered loci, copy-number biology, and cytogenetic limitations.

Relationships to Other Abstractions

Local relationship map for Comparative Genomic HybridizationParents appear above the current abstraction, mutual partners to the right, and children below. Node labels state whether each abstraction is prime or domain-specific; colors identify relation types.Comparative GenomicHybridizationDOMAINPrime abstraction: Ratio — presupposesRatioPRIME

Current abstraction Comparative Genomic Hybridization Domain-specific

Parents (1) — outgoing typed relations

  • Comparative Genomic Hybridization presupposes Ratio Prime

    The test-to-reference signal ratio is the measurement that turns two hybridization channels into relative copy-number evidence; removing it destroys CGH's comparative identity.

Hierarchy path (1) — routes to 1 parentless root

  • Comparative Genomic Hybridization → presupposes Ratio → is a kind of Comparison

Neighborhood in Abstraction Space

Comparative Genomic Hybridization sits in a sparse region of the domain-specific corpus (90th percentile for distinctiveness): few abstractions share its structure, so a faithful description tends to retrieve it precisely.

Family — Unclustered & Miscellaneous (2769 abstractions)

Nearest neighbors

Computed from structural-signature embeddings · 2026-10-25