Comparative Mapping of the Region of Human Chromosome 7 Deleted in Williams Syndrome

BAC/PAC DNA was labeled and hybridized to human G₀/G₁ interphase fibroblast cells or to mouse interphase cells prepared from spleen. The number of distinct fluorescent dots (i.e., a multilobed signal was scored as one dot) per cluster was scored in 100 interphase chromosomes for each probe. Note that an average of 1 is expected for a small, unreplicated single-copy sequence. Large BACs representing known single-copy loci often produce signals with some substructure, which produces a dot count of >1. The presence of some S and G₂ cells in the preparations can also inflate the average dot-count above 1. These factors explain the observation that the average dot-count is 1.2–1.6 for the BACs that we conclude contain single-copy sequences. Of the clones listed, only the human p47–phox-containing BAC (RG350L10) contains sequences that are present in multiple copies. Note that the two human BACs were isolated from the Research Genetics human BAC library (E.D. Green; unpubl.). See Fig. 2 for additional information about the mouse clones.