Determination of the intactness and copy number of theCGM6 transgene. A total of 10 μg of thymus DNA each from a C57BL/6 mouse (lane 1) and from the CGM6-transgenic mouse 5322 (lane 2) was digested with EcoRI, size fractionated, and hybridized with [³²P]-labeled F19632 cosmid DNA. To estimate the number of integrated transgene copies, F19632 DNA corresponding to 75 gene copies per haploid genome was added to 10 μg of C57BL/6 DNA before digestion with EcoRI (lane 3). Cosmid vector fragments and end fragments of the genomic insert of F19632 are indicated by arrowheads and arrows, respectively. The asterisk marks the band, which contains besides an internal EcoRI DNA fragment, the fusion fragment created by the head to tail insertion of the amplified transgene. The mobility and size in kb of the marker fragments is shown in the left margin.