Final answer:
Researchers hypothesized that genetic factors could influence the susceptibility of different sheep breeds to scrapie, leading to varying levels of resistance or vulnerability to the disease.
Step-by-step explanation:
The differential effects of scrapie based on sheep breed led researchers to hypothesize that genetic factors may influence the susceptibility of sheep to scrapie prion disease. Observations indicated that some breeds of sheep showed more resistance to scrapie, while others were particularly vulnerable, leading to the idea that specific genetic variations could affect the disease's impact. This hypothesis has shaped ongoing research into animal and human prion diseases and has prompted scientists to investigate genetic predispositions to such diseases.