Summary of chromatin features observed in somatic cell hybrid clones for the TIMP1 gene. Most subclones and demethylated clones follow the patterns seen for the active and inactive X hybrids that are outlined in bold. A positive (+) designates the presence of the feature, while a negative (-) depicts the absence of the feature, while ND means that the feature has not been examined in that class of clones. The assays used are PCR-based and would detect a small population of cells. DNase sensitivity is listed as the inverse – DNase resistance – as it is the presence of undigested (resistant) DNA that will yield a 'positive' PCR signal. In each category of clones not all clones have been examined for all features. For the clones shaded in grey the results are an amalgamation of results anticipated from an active and inactive X, and we suggest these clones represent a mixed population. This suggestion is generally supported by sub-cloning experiments (see text for discussion). The ongoing H3 acetylation of the Xi/-/M hybrids (highlited in darker grey) cannot be attributed to heterogeneous cell populations, and since it is not seen for demethylated hybrids that have lost TIMP1 expression (t11-az/-/M) we suggest that this modification reflects a predisposing feature of inactive X chromosomes that express TIMP1.