A diversity of alleles for the rhoptry protein encoding genes ROP18, ROP5, ROP16 and ROP17 exist.
RFLP genotyping can readily be used to distinguish allele types among these genes.
Alleles of the ROP18 and ROP5 loci correlate strongly with the virulence of <em>Toxoplasma gondiiem> strains.
RFLP typing of ROP18 and ROP5 loci may be used to identify potentially virulent strains.