How Array CGH Testing Works
Array CGH compares the DNA from a person (the “patient” sample) against known normal DNA (the “control” sample). The patient sample can come from a blood or a prenatal sample. The patient sample DNA is tagged, or labeled, with a specific fluorescent dye color. At the same time, DNA from a control sample is labeled with a different dye color. Equal amounts of the two DNA samples are then mixed and put into the array CGH test.
The array is made from small pieces of DNA attached to a glass slide or tiny beads in a specific order. The patient and control DNA attaches to specific, matching areas on the array. Because there are equal amounts of patient and control DNA, they should attach about the same and the two dye colors should balance each other out (1-to-1 ratio). Analysis of the array depends on a special camera and computer, which carefully measures and records the dye ratio at each array spot.
When there is extra or missing genetic material, it shows up as a dye imbalance. When there is extra DNA in the test sample, there is more of that color than the test sample. When there is missing DNA in the test sample, there is more of the control color. Looking at the array, each array spot can be interpreted as 1) normal, 2) deleted patient DNA, or 3) duplicated patient DNA.
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