Patient's question:
[Male with six fingers. Marries a normal woman and has a daughter, what is the probability that the son is six-fingered.]Doctor's answer:
Polydactyly is one of the most common congenital hand deformities among Chinese people, with the majority of cases occurring on the side of the thumb. It is a hereditary related disease. Among polydactyly, the most common form is hexadactyly (as shown in the figure). Hexadactyly is an X-linked dominant genetic disorder, with the causative gene located on the X chromosome. If the patient is male, the probability of his offspring inheriting the disease with a normal female is 50% (normal sons, hexadactyl daughters). If the patient is female, there are two types of inheritance: complete dominance and incomplete dominance. In complete dominance, the probability of the offspring inheriting the disease is 100%. In incomplete dominance, the probability of the offspring inheriting the disease with a normal male is 50% (equal probability for sons and daughters to be affected). Therefore, the inheritance probability of hexadactyly is high, and it is also sex-linked. As a result, if close relatives marry, the probability of inheriting the disease increases.