Expression of yellow fluorescent protein (YFP) by T. gondii transfected with the pTgmicYFP plasmid. A, Plasmid map of pTgmicYFP. B, Western blot of YFP expressed by the transgenic T. gondii YFP (TgYFP) and wild type T. gondii (WT) using the rabbit anti-GFP antisera and a sheep anti-rabbit IgG HRP-conjugate. C, T. gondii YFP in murine macrophages observed by fluorescence microscopy, confirming the location of YFP by T. gondii YFP. D, Fitness of T. gondii YFP and wild type T. gondii at a ratio of 7:3 in mice.