Genomic DNA digested with II was probed with a radioactively labeled fragment of DNA which detected a II restriction fragment length polymorphism (RFLP) between the Border Collie and Newfoundland grandparents. BC, DNA from the Border Collie grandparent; N, DNA from the Newfoundland grandparent. F1, DNA from the first generation hybrids of the Newfoundland × Border Collie cross; F2, DNA from the progeny of intercrosses between the F1 hybrids; s, white spotted; ns, not white spotted. The presumed genotypes for the locus are shown below the lanes.