Southern blot showing integration pattern of retroviral vector in tail DNA from progeny of recipient W males 5483 and 5486. (A) DNA from three progeny of 5483 (5, 13, and 48) generate bands that migrate to different levels in the gel, indicating three distinct integration sites. A difference in sizes of bands for animals 5483-48 and 5483-70 cannot be distinguished on this gel separation. DNA from animal 5483-13 generates two bands and may have two sites of vector integration. DNA from two progeny of 5486 (4 and 15) generate bands of different sizes. Bands for progeny 15, 18, and 37 of W male 5486 on this gel appear similar. DNA from only one offspring of 5655 (5655-3) was examined. Nontransgenic mice display no band. (B) Progeny 8, 9, and 13 from 5483-5♀ (Left) have the same band migration and thus vector integration site as the parent, indicating stable integration of the transgene. Progeny 1 and 2 from 5486-4♂ (Right) have the same integration site as the parent, again indicating stable integration of the transgene. Results of staining for lacZ are indicated by + or − .