LAWRENCE LIVERMORE NATIONAL LABORATORY / SCIENCE PHOTO LIBRARY LAWRENCE LIVERMORE NATIONAL LABORATORY / SCIENCE PHOTO LIBRARY
Normal result in the prenatal screening of Down syndrome: fluorescence in situ hybridisation (FISH) micrograph of chromosomes from sampled cells of a normal fetus. FISH is being applied to prenatal detection of Down syndrome (Trisomy 21). Here, chromosome 21 DNA appears yellow when stained with fluorescein; the remaining cellular DNA appears red from staining with propidium iodide. Normal cells with 2 copies of chromosome 21 usually show 2 yellow domains; Down syndrome cells have 3 copies of chromosome 21 & usually show 3 yellow areas. Variance due to domain overlap is corrected by statistical methods.
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