When a brother marries his sister, it is consanguineous marriage. The marriage law stipulates that it is forbidden for lineal blood relatives to get married within five generations. It is illegal and immoral for a brother to marry his sister, and the marriage registration office of the Civil Affairs Bureau will not handle the registration formalities for him. Even if the marriage has been registered, the civil affairs department will take back the marriage certificate.
Inbreeding has the following hazards: 1, which greatly increases the incidence of recessive genetic diseases in children. 2. Increase the incidence of polygenic diseases in children. 3, increase the chance of child deformity.