Can two sisters have different blood groups?
Yes this is possible. For a full explanation of blood group inheritance, see: http://www.purchon.com/biology/abo.htm Rh factor is dominant/recessive. Both father and mother are Rh+, so both children inherit at least one Rh+ gene from either parent, and may have inherited both Rh+ genes. The Mother has no genes for A or B antigen blood. The father has one B and one O gene, so one child ended up with a B from the father, and O from the mother. The other child inherited an O from their father and an O from their mother. O = absence of either A or B antigen gene.
