Blood genotype refers to the genetic makeup of the blood in an individual. Genotypes are in pairs, and there are five of them: AA, AS, AC, SS and SC. Persons with AA, AS and AC are usually normal physically while those with SS and SC manifest with sickle cell disease.
Those with genotypes AS and AC are said to have sickle cell trait. They live normal life like those with genotype AA because the genes for S and C do not manifest their characters in the presence of the genes for A.
In individuals with SS and SC genotypes, the cells assume an abnormal shape, especially in the presence of low oxygen tension. This makes it difficult for them to pass through tiny blood vessels, especially at the junctions of arteries and veins (capillaries).
As a result of this, they get trapped there and make it difficult for blood to circulate round. The resulting lack of oxygen supply to the parts of the body blocked by the sickle cells and inability to clear the waste products of metabolism from there result in pain and organ dysfunction.
The resulting condition is called sickle cell disease because the cells assume the shape of a sickle and are somehow rigid, unlike the normal red blood cells which are usually round and flexible.
The shape and flexible nature of normal red blood cells make it easy for them to be able to pass through small blood vessels and supply nutrients and oxygen to all parts of the body.
Conversely, the rigid nature of sickle cells makes it difficult for them to manoeuvre small blood vessels, thereby blocking them and preventing nutrient and oxygen supply to body organs.
Importance of knowing one’s genotype – Knowing your genotype is very important in determining your marriage partner. This is important because of the risk of sickle cell disease in children born to parents with sickle cell trait.
A child inherits its genetic composition from both parents. It is important to have adequate information on genotype compatibility in order to avoid a lifetime mistake with devastating effects of sickle cell disease on your offspring.
Genotype AA – An individual with genotype AA can get a partner from any other category of blood genotype with little or no risk of having offspring with sickle cell disease.
Genotype AS – An individual with genotype AS can get a partner from those with AA only, to be guaranteed of having offspring free of sickle cell disease.
Genotype AC – Just like those with genotype AS, an individual with genotype AC is also restricted to having a partner from those with genotype AA to be sure of having children free of sickle cell disease.
Genotypes SS and SC – Individuals with these blood genotypes have to choose partners from those with genotype AA in order to have children free of sickle cell disease.
Invariably, only persons with genotype AA can freely choose partners from any other group.
According to Mendelian’s law of inheritance, the following are the resulting genotypes of the offspring when persons with each of these genotypes takes a life partner from the other group:
| Parents’ genotype | Possible genotypes of offspring | Remark |
| AA + AA | AA, AA, AA, AA | Excellent (all children are normal) |
| AA + AS | AA, AA, AS, AS | Good (all children are normal) |
| AA + AC | AA, AA, AC, AC | Good (all children are normal) |
| AA + SS | AS, AS, AS, AS | Fair (all children are normal) |
| AA + CC | AC, AC, AC, AC | Fair (all children are normal) |
| AS + AS | AA, AS, AS, SS | Bad (children at risk of sickle cell disease) |
| AC + AC | AA, AC, AC, CC | Bad (children at risk of sickle cell disease) |
| AS + AC | AA, AC, AS, SC | Bad (children at risk of sickle cell disease) |
| AS + SS | AS, AS, SS, SS | Bad (children at high risk of sickle cell disease) |
| AS + SC | AS, AC, SS, SC | Bad (children at high risk of sickle cell disease) |
| SS + SS | SS, SS, SS, SS | Very bad (all children will come down with sickle cell disease) |
| SS + SC | SS, SS, SC, SC | Very bad (all children will come down with sickle cell disease) |
