who are identical twins; both have short fingers. Heather's two younger sisters have normal fingers. Heather's mother has normal fingers, and her father has short fingers. Heather's paternal grandmother has short fingers; her paternal grandfather, who is now deceased, had normal fingers. Both of Heather's maternal grandparents have normal fingers. Heather marries Tom, who has normal fingers; they adopt a son named Jeffrey who has normal fingers. Jeffrey's biological parents both have normal fingers. After adopting Jeffrey, Heather and Tom produce two children: an older daughter with short fingers and a younger son with normal fingers. What is the most likely mode of inheritance for short fingers in this family? If Heather and Tom had another biological child, what is the probability that this child will have short fingers?