Possible patterns of nucleosome positioning. Diagrams show four possible combinations for the local and relative position of nucleosomes. (A) Nucleosomes occupy reproducible positions in all cells and are regularly spaced relative to one another. (B) Nucleosomes are regularly spaced relative to one another, but have no strong tendency to occupy the same position in different cells. (C) Nucleosomes occupy the same position in all cells but are not regularly spaced relative to one another. (D) Nucleosomes neither occupy the same position in all cells nor have regular spacing relative to one another.