Evaluation of the TPO competitor DNA. (A) PCR products after purification and reamplification. Lane t, 404-bp TPO product generated by 5′ and 3′ TPO primers; lane c, 318-bp competitor, produced by 5′ composite and 3′ TPO primers and reamplified with 5′ and 3′ TPO primers. (B) Amplification of TPO cDNA and TPO competitor cDNA over eight steps of twofold dilution appears to be linear by visual inspection. Lanes 1 through 8, TPO competitor dilution series; lanes 9 through 16, cDNA dilution series; m, 100-bp DNA ladder; (−), negative PCR control, all reagents except template.