Hapsburg family tree: inheritance of the "Hapsburg Lip"
Mandibular prognathism is the name of a genetic condition in which growth of the maxilla (upper jaw) is retarded with respect to the the mandible (lower jaw), so as to produce a forward-jutting chin, rolled-out lower lip, and a cross-bite of the incisors. The phenomenon is called the 'Hapsburg Lip' because of its occurrence in multiple generations of members of the European royal House of Hapsburg, as documented in their portraits over 200 years [above]. Kings of Spain Philip IV and his son Charles II are the poster children, along with Leopold I of Austria. The trait is inherited as a single-gene autosomal dominant with incomplete penetrance (~ 0.90), and shows up frequently because of extensive intermarriage and inbreeding among different branches of the royal families of Europe. Queen Isabella I & King Ferdinand II of Castile & Aragon, Columbus' patrons on his voyages to America, are early case. Artists' portraits likely'improved' the appearance of their subjects in some cases.
HOMEWORK: Redraw the portrait gallery above as a pedigree. Ascertain how many generations over what period are involved. Show that inheritance is consistent with an autosomal recessive. (Note that only affected persons are shown: this causes an ascertainment bias).