Blood chimeric twins: an example of blood cell chimerism

A man and his twin sister were found to have two types of circulating red cells. The man had 89% A1 cells of his own and 11% A1B cells derived from his sister. The woman had 12% A1B cells of her own and 88% A1 cells derived from her brother. The two lines of red cells also had different Duffy and Kidd groups. The lymphocyte karyotype in the brother was 68% XY and 32% XX, and that in the sister was 60% XX and 40% XY. The possible mechanisms for producing different proportions of red cells and lymphocytes are discussed.