Fluorescently labeled avidin, which binds biotin, was used to visualize the positions of the two copies of chromosome 7 in nuclei. Note that the two chromosomes occupy two nonoverlapping regions in the nucleus. This suggests organization of the interphase chromatin into specific domains. Recall that this chromatin is not visible by light microscopy so other experimental approaches are needed to visualize it. The Eukaryotic cell cycle.
Chromatin contains small amounts of other proteins besides histones and scaffold proteins.
Banding of metaphase chromosomes helps map the positions of genes and translocations. Chromosomes can be treated in a way that allows for reproducible staining patterns with Giemsa stain for example. The physical and chemical basis for this patterning is unclear, but useful nevertheless as reference points on chromosomes and as ways of identifying individual chromosomes. For example, certain chromosomal translocations are characteristic of specific genetic diseases and specific types of cancer. Here are shown leukemia cells of a particular type of leukemia in which the presence of two abnormal chromosomes are created from a translocation between normal chromosomes 9 and 22.