Blood Types The gene for producing blood has three variants: - Blood cells include the A antigen - Blood cells include the B antigen - Blood cells have neither (inactive "O" version). - Separately: do you have the Rh factor? (+ or -)

Blood Types Frequencies Typefrequency (US)note O-6.6 %universal donor O+37.4 % A-6.3 % A+35.7 % B-1.5 % B+8.5 % AB-0.6 % AB+3.4 %universal recipient

Genes Each of a person’s two genes are either A, B, O (with A,B both dominant over O). Separate gene: Rh+ or Rh-. Example: If mother phenotype is B- and father phenotype AB-, what can children be? Mother genotype: BB or BO; --. Father genotype: AB; --. If mother BB, children are AB-- or BB--. If mother BO, children are AB--,BB--,AO--,BO--.

Why it matters If your blood does not have the A antigen but you get a transfusion that does, your body sees the A as "enemy" – rejects. What if pregnant, and blood type of child differs from mother?! - A/B/O okay -- antibodies don't pass placenta. - But anti-Rh+ antibodies can cross; dangerous if: mother Rh-, and mother previously exposed to Rh+, and baby is Rh+.