As the frequency of medulloblastomas was not decreased much more in Ptch1Δ/+Pn-1Δ/Δ than Ptch1Δ/+Pn-1Δ/+ mice (Fig 3, compare orange to red line), the subsequent analysis focused on Ptch1Δ/+Pn-1Δ/+ mice. The gene discussed is PTCH1; the disease is medulloblastoma.