In these aspects, pyrimethamine used for treating toxoplasmosis blocks the synthesis of tetrahydrofolic acid from dihydrofolate reductase (DHFR) by effectively inhibiting the dihydrofolate reductase in T. gondii, which inhibits consistently synthesis of the DNA and/or RNA in the proliferation of protozoa species, including malaria. The gene discussed is DHFR; the disease is toxoplasmosis.