[i] Comparison of α-satellite DNA-containing restriction fragment sizes between two cell lines. For each restriction digest (exceptBglI, where multiple fragments were summed; see Figs. 1 and2), X chromosome-specific α-satellite probe hybridized to a single pulsed-field gel fragment, containing the intact array along with variable amounts of flanking DNA, depending on the restriction enzyme. Although the two X chromosomes examined have very different array lengths, the positions of rare-cutting restriction sites relative to the array edges are similar. This is evidenced by the amount of non-α-satellite (flanking) DNA present on a given fragment, which is estimated by subtracting the total array size from the restriction fragment size.