Inheritance of Y-linked Genes

Y-linked, or holandric, genes sit in the non-homologous region of the Y chromosome — the part with no counterpart on X — and because every son inherits his Y chromosome directly and only from his father, these genes pass in an unbroken father-to-son line and never appear in daughters at all (a daughter, inheriting only her father's X, is simply never exposed to his Y-linked alleles). The textbook's human example is hypertrichosis — excessive hair growth on the pinna (outer rim) of the ear — which is transmitted directly from father to son exactly this way. Holandric inheritance is the cleanest possible pedigree pattern to recognise: if every affected individual acr …