According to China's Marriage Law and Civil Code, those who belong to direct blood relatives or collateral blood relatives within three generations are considered close relatives and are not allowed to register marriage. Direct blood relatives refer to the relationship between parents and children, as well as between grandparents and grandchildren; Within three generations, collateral blood relatives refer to relationships between uncles (aunts) and nephews (daughters), uncles (aunts) and nephews (daughters), as well as relationships between brothers (sisters) and cousins (sisters) that cannot be married.
The harm of consanguineous marriage
Couples who marry close relatives may inherit the same gene from their common ancestor and pass it on to their children. If this gene is inherited in an autosomal recessive manner, their children may develop the disease due to homozygous mutations, thus increasing the risk of certain autosomal recessive inherited diseases. The incidence of recessive genetic diseases in offspring of consanguineous marriages will be 150 times higher than that in offspring of non consanguineous marriages. According to the survey, the incidence rate of polygenic diseases such as congenital heart disease, anencephaly, spinal cord fission and so on in the offspring of close relatives married is about 1.64%, higher than 0.57% in the children of non close relatives married.