How is your blood type determaned?
There are two important blood types: the ABO blood type and the
Rhesus blood type. ABO is the A, B, AB, or O blood type, and the
Rhesus type is the + or - usually written after the ABO blood type
(eg. AB+ or O-). At the level of your blood, blood type is
determined by proteins present on the surface of red blood cells,
which circulate around your body delivering oxygen to cells. On the
surface of red blood cells is a combination of three surface
proteins: A, B, and Rhesus. Blood types code for the presence or
absence of these proteins. Blood type A have A type surface
proteins but lack B. Blood type B lacks A but has B proteins. Blood
type AB has both, and Blood type O has neither A nor B. Rhesus
positive exhibit the Rhesus protein, while Rhesus negative lack it.
It is these proteins which determine which types of blood you can
receive safely. Individuals with A type blood cells cannot be
exposed to B type surface proteins safely, so B and AB blood is off
the cards for them. O negative blood lacks any of these proteins so
can be transfused into any patient, hence the term "universal
donor". It is your genes which determine which of these proteins
are expressed. As with the majority of genes you have two copies of
both the ABO and Rhesus genes, one copy from your mother and one
from your father. From each parent you inherent either an A, a B,
or an O gene, and also either a Rhesus positive (Rh+) or a Rhesus
negative (Rh-) gene. The combination of the two genes you have
determines your blood type as follows: AA or AO = A Blood type BB
or BO = B Blood type AB = AB blood type OO = O Blood type Rh+Rh+ or
Rh+Rh- = Rhesus positive Rh-Rh- = Rhesus negative
