For example, sheep homozygous for PrP with V136R154Q 171 or A136R154Q 171 show opposite patterns of susceptibility to scrapie strains SSBP1 and CH1641 [62], [63], and in vitro generation of PrPres in PMCA reactions agreed with the in vivo resistance observed [64]. This evidence concerns the gene PRNP and scrapie.