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The four main blood groups are the following:

1.Type A. This type of blood has a marker known as "A."
2.Type B. This type of blood has a marker known as "B".
3.Type AB. This type of blood has both A markers and B markers.
4.Type O. This blood type has no A or B markers.

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Some people have an extra marker, called Rh factor, in their blood. Since the major blood groups (A, B, AB, and O) may or may not have the Rh factor, scientists also classify the blood as "positive" (meaning that it has the Rh factor) or "negative" (without the Rh factor).

Having one of these markers (or none of them) does not make a person's blood healthier or stronger than the others. They are nothing more than genetic differences, such as having green eyes instead of blue ones or straight hair instead of curly ones.

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The main groups are divided into the following

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The main groups are divided into the following

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O negative. This type of blood has no A or B markers and does not have the Rh factor either.
O positive. This type of blood has no A or B markers but it does have the Rh factor. It is one of the two most frequent types of blood (next to A positive).
A negative. This type of blood only has the A marker
A positive. This blood type has the A marker and the Rh factor, but it lacks the B marker. Along with the positive O, it is one of the two most frequent blood types.
B negative. This type of blood only has the marker B.
B positive. This blood type has the B marker and the Rh factor, but it lacks the A marker.
AB negative. This type of blood has markers A and B, but lacks the Rh factor.
AB positive. This type of blood has the three markers: A, B and Rh factor.

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What groups do they donate to and what do they donate to?

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What groups do they donate to and what do they donate to?