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Blood Groups
Blood Groups
Blood Groups are the distinguishing of blood by their
antigenic properties. These properties are determined by the substances found on
the surface of the red blood cells. There are approximately 200 blood group
substances identified and categorized into 19 distinct systems. The most common
system is the ABO system.
What is the ABO system?
The ABO system consists of people with blood groups A, B,
AB or O. Individuals may contain the A, B or both or none of the antigenic
substances. Any individual that lacks any one of the antigens will develop
antibodies against it at birth. For example, a person with blood type A will
develop anti-B agglutinants. Agglutinants causes blood to clump together and can
possibly form a blood clot making the blood extremely viscous.
This is why practitioners must be certain of your blood
type before you can make a blood donation or before you receive any donated
blood from a donor. A mix-up in the blood types during transfusion could be
fatal to the receiver as the blood would agglutinate within him forming numerous
blood clots eventually leading to death.
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What are genotypes and how are they related to blood
groups?
Genotypes are the genetic make-up of an organism, the genes
and its respective alleles. Your blood group is greatly dependant upon your
parent’s blood groups. Each person has two copies of gene coding for their ABO
blood group, one maternal while the other paternal in origin. A and B blood
groups have been observed by scientists to be dominant over the O blood group. A
and B blood groups were also found to be co-dominant, which means that they can
co-exist and if a person has genes for both, he could possess both the A and B
blood group antigens, hence he does not form any antibodies and can take in all
types of blood.
Below provides a table summary of the blood group, the red
cell antigens and possible inherited genotypes :
| Blood group |
Red Cells Antigens |
Antibodies |
Genotypes |
| A |
A Antigens |
Anti-B antibodies |
AA or AO |
| B |
B Antigens |
Anti-A antibodies |
BB or BO |
| AB |
AB Antigens |
None |
OO |
| O |
None |
Anti A and Anti B antibodies |
AB |
Note that the genotypes come in pairs. They represent the
double ABO gene coding that we have from our parents.
What is the Rhesus Factor?
The Rhesus factor is named after the Rhesus monkey that it was named after. Irregardless of our blood type, we all have a pair of rhesus genes. Depending on whether we are rhesus positive or negative, the rhesus factor will affect our heredity line.
The rhesus positive is commonly known
as D and the rhesis negative is commonly known as d.
How is it passed through heredity?
As mentioned, we all inherit two rhesus genes, one from each parent. A person is rhesus negative if they have inherited a d gene from each parent (d/d) A person is rhesus positive if they have inherited either a D gene from both parents or a D gene and a negative d gene.
If you have inherited a rhesus positive gene and a rhesus negative gene, you are most likely to be rhesus positive as the D gene is more dominant as compared to the d gene. Hence it is possible to it is possible to have a rhesus negative baby and a rhesus positive father.
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Problems with Pregnancy
If the mother is rhesus negative and has a rhesus positive baby for the first time, there would be no complication whatsoever as her body has not developed any antibodies what the body recognizes as “foreign” which in this case refers to the baby. However, in her second pregnancy, if the baby is still tested to be rhesus positive, the mother’s body would have already developed antibodies against the rhesus negative factor and against the baby, resulting in pregnancy complications.
To prevent this from happening, rhesus negative mothers are usually given anti-D injections after the first pregnancy. However, anti-D
injections are of no use once the pregnancy has started.
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