NCI Dictionary of Genetics Terms

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Welcome to the NCI Dictionary of Genetics Terms, which contains technical definitions for more than 150 terms related to genetics. These definitions were developed by the PDQ® Cancer Genetics Editorial Board to support the evidence-based, peer-reviewed PDQ cancer genetics information summaries.

When chromosomes at a particular stage in cell division are stained using one of several laboratory techniques, a specific pattern of light and dark stripes (bands) appears when the chromosomes are viewed through a microscope; the banding pattern assists in assigning each chromosome its particular number and evaluating its structure.