6 25 pm pst [ blood and DNA ]
At dinner on Tuesday, my father asked me a favor.
"Can you go on the computer and find out about DNA
testing for me?"
"For a paternity test for a client?" I guessed.
"Yes."
I agreed and we launched into a discussion on DNA and
later on blood types. My dad thought that a mother and her unborn child
shared a blood stream. I thought they didn't, with nutrients diffusing
across a membrane. I said I thought there was only one blood type that
was problematic for a mother and child to have different from each other.
Yesterday I sent my dad a long e-mail with information on:
My dad was impressed and suggested I do internet
research for a living. I chuckled to myself and decided that I'll have to
introduce him to google.com soon. Today I got curious about blood types.
And now all about blood typing. All of the following
information is taken from:
Human blood is classified according to the presence or
absence of certain markers, called antigens, on the surface of red blood
cells.
If your red blood cells have:
- The A antigen, you have type A blood.
- The B antigen, you have type B blood.
- Both the A and B antigens, you have type AB blood.
- Neither the A nor B antigen, you have type O blood.
The various ABO blood groups occur in the average
population of the US in the following proportions (these percentages vary
within different ethnic groups):
- 45% are type O
- 42% are type A
- 10% are type B
- 3% are type AB
Rh blood typing determines the presence (+) or absence
(-) of the Rh antigen (also called the Rh factor). If your red blood
cells:
- Contain the Rh antigen, your blood is Rh-positive.
- Do not contain the Rh antigen, your blood is Rh-negative.
- Contain the A and Rh antigens, your blood type is
A-positive (A+). If your blood contains the B
antigen but not the Rh antigen, your blood type is
B-negative (B-).
The various blood groups occur in the average
population of the US in the following proportions:
- 36% are type O+
- 9% are type O-
- 34% are type A+
- 8% are type A-
- 8% are type B+
- 2% are type B-
- 2.5% are type AB+
- 0.5% are type AB-
Type O-negative blood does not have any antigens and is
called the "universal donor" type because it can be given to a person of
any blood type. Type AB-positive blood is called the "universal recipient"
type because a person who has it can receive blood of any type. Minor
antigens (other than A, B, and Rh) that occur on red blood cells can
sometimes also cause problems and may be checked for a match before a
blood transfusion.
Blood you receive in a transfusion must not contain an
antigen that is not already present on your own red blood cells. A normal
immune system will destroy red blood cells that contain an antigen
different from what is naturally present on your own blood cells.
Transfusion of an incompatible blood type is more dangerous if you have
previously been given an incompatible blood type, since the transfusion
reaction produces more rapid and extreme destruction of the new blood
cells with repeated exposures.
Rh blood typing is especially important for pregnant
women. A woman who is Rh-negative can become pregnant with an Rh-positive
child if the child's father is Rh-positive. The woman can then become
sensitized to the Rh antigen if her blood and her unborn child's (fetus's)
blood mix (Rh sensitization). There is no danger to the mother and
usually no harm to the first Rh-positive child. However, future
Rh-positive children are in danger of having their red blood cells
destroyed before birth by the mother's immune system. This danger can
usually be prevented by giving the mother a vaccine (Rh immunoglobulin
vaccine, Rhogam) that prevents her immune system from attacking the blood
of her fetus.
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