Search: blood type
Why: On "Lost" this week, Kate said she is a "universal blood donor."
Answer: A blood type is a classification based on the presence or absence of inherited antigenic substances on the surface of red blood cells (RBCs). These antigens may be proteins, carbohydrates, glycoproteins, or glycolipids, depending on the blood group system.
In the common ABO System, there are 3 variations of the blood type gene: A, B, and O. Since we all have 2 copies of these genes (1 from each parent), there are 6 possible combinations: AA, BB, OO, AB, AO, BO.
Maybe you can decipher this paragraph about the genes themselves:
The theory that explains how these antibodies are developed states that antigens similar to the A and B antigens occur in nature, including in food, plants and bacteria. After birth an infant gut becomes colonized with normal flora which express these A-like and B-like antigens, causing the immune system to make antibodies to those antigens that the red cells do not possess. So, people who are blood type A will have Anti-B, blood type B will have Anti-A, blood type O will have both Anti-A and Anti-B, and blood type AB will have neither.Source: Bloodbook.com
The More You Know: Here is how common each blood type is: