Unlike canon, Voldie’s father in HPMoR could have lacked magical phenotype, but must have had one magic allele and at least some distant wizard/like ancestors, because of inheritance of magic in HPMOR (which is different from canon). If somebody sequenced the DNA of HPMoR version of Voldie’s father, they would find the squib genetic make-up, not muggle.
That is just a side technical note, though. The father was probably sufficiently unrelated to the mother’s family, which probably really helped with the inbreeding problems.
Unlike canon, Voldie’s father in HPMoR could have lacked magical phenotype, but must have had one magic allele and at least some distant wizard/like ancestors, because of inheritance of magic in HPMOR (which is different from canon). If somebody sequenced the DNA of HPMoR version of Voldie’s father, they would find the squib genetic make-up, not muggle.
That is just a side technical note, though. The father was probably sufficiently unrelated to the mother’s family, which probably really helped with the inbreeding problems.