Quantification of the number of MSG genes by real-time PCR experiments. Donor genes were amplified using primers CRJE-RT and C1 (Additional file 3, Table S2). The UCS was amplified with UCS primer -145 and primer α-CRJE (Additional file 3, Table S2). At least three independent PCR reactions were performed with a given primer pair. The two bars of different shades show data obtained from P. carinii populations isolated from two different rats.