What is the principle of spectral karyotyping?

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The principle of spectral karyotyping (SKY) is based on fluorescence in situ hybridization (FISH) using chromosome-specific DNA probes, each labeled with a unique combination of fluorochromes. Although only five different fluorescent dyes are used, they are mixed in specific ratios so that each chromosome gets a unique combination of colors. This creates a specific spectral signature for every chromosome.

These labeled probes are hybridized to metaphase chromosomes fixed on a glass slide. After hybridization, a fluorescence microscope with a spectral imaging system is used to detect the signals. The spectral imaging system captures the wavelength emission pattern from each chromosome. Then, spectral unmixing algorithms are applied through a computer system to separate and identify the unique color of each chromosome.

In short, principle of spectral karyotyping works on the idea that:

Each chromosome is labeled with a unique color code using combinations of fluorescent dyes.
The microscope detects the mixed fluorescence from each chromosome.
Software then analyzes the spectral signature and assigns a false color to each chromosome based on its fluorochrome mixture.

Because of this principle, spectral karyotyping allows all 24 human chromosomes (22 autosomes + XX or XY) to be simultaneously visualized in different colors, making it easy to detect chromosomal abnormalities like translocations, deletions, duplications, or complex rearrangements.

So, the core principle involves three key steps:

Probe labeling with unique combinations of fluorochromes
Hybridization of probes to metaphase chromosomes
Spectral detection and image processing to assign unique colors to each chromosome based on their spectral pattern

This combination of molecular labeling and digital imaging forms the basic working principle of spectral karyotyping.

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