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, six-finger syndrome is the most prevalent form (as shown in the figure). Six-finger syndrome 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 from a normal female is 50% (normal sons, six-finger syndrome daughters). If the patient is female, there are two types of inheritance: complete dominance and incomplete dominance. In complete dominance, the probability of offspring inheriting the disease is 100%. In incomplete dominance, the probability of the child inheriting the disease from an unaffected male is 50% (equal risk for boys and girls). Therefore, six-finger syndrome has a high inheritance probability and is also sex-linked, so the risk of the disease increases with consanguineous marriages.