Determination of transgene copy number by semi-quantitative RT-PCR. Semi-quantitative RT-PCR experiments were performed on the initial construct (standard) or samples from mouse tail DNA preparations. A) Linear relation between template input (amount of the standard DNA) and measured band intensities of PCR products. B) Calculated copy numbers of five different transgenic mice. From each sample, the mean value and the standard deviation are shown. Experiments were performed in duplicate.