Array Comparative Genomic Hybridization (Array CGH) is a powerful technique used to detect genetic imbalances, such as deletions, duplications, and amplifications, in the DNA. It is particularly valuable in identifying submicroscopic chromosomal abnormalities that traditional methods, like karyotyping, may miss. Here’s a breakdown of how Array CGH works:
1. DNA Extraction
- The first step involves extracting DNA from come funziona array cgh both the test sample (usually from the patient) and a reference sample (often from a healthy individual). These DNA samples serve as the basis for comparison in the Array CGH process.
2. DNA Labeling
- Both the test DNA and the reference DNA are labeled with different fluorescent dyes. Typically:
- The test DNA is labeled with a red fluorescent dye.
- The reference DNA is labeled with a green fluorescent dye.
- This allows the two DNA samples to be distinguished based on the color intensity during the analysis.
3. Hybridization to Microarray
- The labeled DNA samples (test and reference) are then mixed together and hybridized onto a microarray. The microarray consists of thousands of DNA probes—small pieces of DNA that represent specific regions of the genome.
- These probes are attached to a solid surface, such as a glass slide or a chip, and are designed to specifically bind (hybridize) to complementary sequences in the DNA samples.
4. Scanning the Microarray
- After the hybridization process, the microarray is scanned using a specialized fluorescence scanner. This scanner detects the intensity of the fluorescent signals emitted by the test and reference DNA samples.
- In regions where there is an equal copy number of DNA between the test and reference samples, the fluorescence from both samples will appear in equal intensity (i.e., a balanced signal of red and green).
- In regions where the test DNA has more copies than the reference DNA (indicating a duplication), the red fluorescence will be stronger. Conversely, in regions where the test DNA has fewer copies (indicating a deletion), the green fluorescence will dominate.
5. Analyzing the Data
- The fluorescence intensity data is then analyzed to identify genomic imbalances, such as deletions, duplications, or amplifications.
- Red signal dominance: Suggests a duplication in the test DNA (extra copies of a region).
- Green signal dominance: Indicates a deletion (loss of a chromosomal region).
- Equal signal: Suggests no imbalance, meaning the test sample and reference sample have similar copy numbers in that region.
6. Interpretation of Results
- The data is processed and visualized in the form of a genomic map, showing the relative copy number variations (CNVs) across the genome. These CNVs can be compared to a reference genome to pinpoint areas where imbalances are present.
- Any detected imbalances—whether deletions, duplications, or amplifications—are then correlated with known genetic disorders or diseases. This helps to identify the potential genetic causes of a patient’s symptoms or condition.
Key Points to Remember
- Array CGH works by detecting genomic imbalances (gains or losses of genetic material).
- The technique uses fluorescent labeling of two DNA samples (test and reference) and compares their hybridization patterns on a microarray.
- It provides a high-resolution analysis that can detect small chromosomal abnormalities that might be missed by traditional cytogenetic techniques.
- Copy number variations (CNVs) are identified by differences in fluorescence intensity, which indicate regions of the genome with deletions, duplications, or amplifications.
This powerful diagnostic tool is widely used in cancer genomics, genetic disorder diagnosis, and prenatal screening, helping clinicians and researchers better understand the genetic basis of various conditions.