Expression of human β globin by adult transgenic mice. Multiplex RT-PCR was performed on peripheral blood (PB) RNA from adult F₁ transgenic mice. For each line, undiluted PB cDNA (first lane) and cDNA diluted 1:10 (second lane) were used as PCR templates to ensure that the assay was in the linear range of amplification. Both human β-globin– and adult mouse β-globin (β major + β minor)–specific primers were used in each reaction. Twenty cycles of PCR were performed in the presence of ³²P-dATP, and the reaction products were separated on a 5% acrylamide gel. Levels of human β globin relative to adult mouse β globin were quantitated by phosphorimaging. Expression of human β globin as a percentage of adult mouse β-globin expression per gene copy is denoted for each founder line below each pair of lanes.