Knowing your genotype is an important thing to do before choosing a life partner. This is because marrying a person who has genotype incompatibility with you may result in giving birth to offspring with certain diseases, such as sickle cell disorders.
What is a Genotype?
A genotype is the set of genes in our DNA that is responsible for a certain trait. It is also defined as the set of alleles or gene variants in an individual. It is a completely inherited generic identity, and is unique to each individual. Furthermore, it has coded instruction, has presence in all the cells, and is passed during cell division to the next generation.
Human beings are a diploid organism, which means they have two alleles at a given locus, with each of them coming from both the father and the mother. Genotype, and epigenetic factors (environmental, behavioral factors affecting the gene) determine the phenotype.
The main difference between genotype and phenotype is that while genotype is an internally coded inherited information, phenotype is outward physical manifestation like observable features, physical parts, and behaviors.
Types of Genotypes
As we explained earlier, genes are hereditary materials passed to the offspring from the parents. They are stored in the molecules of DNA called chromosomes.
Each of our parents have two copies of their genes, but they can only pass one copy to their offspring. These genes determine our traits like color of skin, hair, eyes, etc. This is also the same for the genes for hemoglobin.
Hemoglobin is the part of the red blood cells that moves oxygen to organs and tissues in the body. Hemoglobin A is the most common type of hemoglobin. However, changes in the body can lead to changes in hemoglobin A, resulting in other types such as Hemoglobin C, and Hemoglobin S. The type of hemoglobin we inherit give rise to our genotype.
There are six distinct types of genotypes. The four main common types are AA, AS, AC, SS, while the rare types are SC, and CC.
This group inherits the normal hemoglobin – Hemoglobin AA from both parents. AA is the most common genotype, and they can marry any other types like AS, SS, AC.
- AA can marry AA: AA + AA = AA, AA, AA, AA (Excellent)
- AA can marry AS: AA + AS = AA, AS, AA, AS, (Good)
- AA can marry SS: AA + SS = AS, AS, AS, AS, (Fair)
- AA can marry AC: AA + AC = AA, AA, AA, AC. (Good)
The AS genotype, or Hemoglobin AS, has inherited one normal Hemoglobin A from one parent, and Hemoglobin S from the other parent. The AS is also called Sickle Cell trait, however they do not suffer from any of the sickle cell anemia symptoms. AS occurs mostly in the Black race.
AS can only marry AA, as marrying another AS can increase the chances of having kids with sickle cell anemia. The ratio is one out of four will have sickle cell anemia (SS), two out of four will have sickle cell trait (AS), while one out of four will have normal hemoglobin (AA).
If AS marry AA, there are no chances of Sickle Cell Anemia (SS). The ratio is two out of four having normal hemoglobin (AA), while the other two out of four will have sickle cell trait (AS).
- AS can marry AA: AA + AS = AA, AS, AA, AS, (Good)
- AS should not marry AS: AS + AS = AA, AS, AS, SS, (Very Bad)
- AS should not marry AC: AS + AC = AA, AC, AS, SC. (Bad; Advice needed)
- AS should not marry SS: AS + SS = AS, SS, SS, SS, (Very Bad)
The SS genotype, also called Sickle Cell Anemia, occurs when the offspring inherits the Hemoglobin S from both parents. This anemia causes the release of high quantity of oxygen by the hemoglobin, causing changes in the shape of red blood cells from round shaped to sickle.
This sickle cell shaped blood cells die quicker than normal red blood cells, hence people with the anemia do not receive enough oxygen to the body tissues and organs. They also suffer from symptoms such as shortness of breath, paleness, tiredness, and vaso-occlusion. Vaso-occlusion results in the sickle red blood cells to block blood flow to the tissues, resulting in pain and damage to organs (“sickle cell crisis”)
Sickle cell anemia is common in the Black race, but can be found in Asia, Middle East, Latin America, and the Mediterranean regions. SS genotype should only marry AA genotype.
- SS can marry AA: AA + SS = AS, AS, AS, AS, (Fair)
- SS should not marry AS: AS + SS = AS, SS, SS, SS, (Very Bad)
- SS should not marry AC: AC + SS = AS, AS, SS, SS, (Very Bad)
- SS should not marry SS: SS, SS, SS, SS, (Very Bad)
This genotype, also called Hemoglobin C Trait, occurs when a person inherits a normal Hemoglobin A from one parent, and Hemoglobin C from another parent, resulting in Hemoglobin C trait (AC). AC is less common, but occurs in some percentage of Black people. There are no health problems associated with it.
- AC can marry AA: AA + AC = AA, AA, AA, AC. (Good)
- AC should not marry AS: AS + AC = AA, AC, AS, SC. (Bad; Advice needed)
- AC should not marry SS: AC + SS = AS, SC, SC, SC, (Very Bad)
- AC should not marry AC: AC + AC = AA, AC, AC, CC. (Bad; Advice needed)
If a person inherits Hemoglobin C from both parents, the person gets Hemoglobin C disease (CC). The disease has symptoms such as mild to moderate anemia, enlarged spleen, gallstones, and jaundice. This disease is rare, and not all CC persons suffer the disease symptoms.
Those with CC genotype should only marry those with AA.
If a person inherits genes for Hemoglobin S from one parent, and Hemoglobin C from the other parent, the person will have sickle cell Hemoglobin C disease (SC disease). This disease may have symptoms that range from mild to severe, and are similar to the symptoms in sickle cell anemia or Hemoglobin C disease. However, they are less severe. Symptoms include damage to hip joint, retina.
While some symptoms appear in the first 10 years of life, others appear later or during pregnancy, causing complications. It is a rare type.
SC should only marry AA.
Can the Genotype Changed?
Sickle cell disease is one of the inherited blood disorder that is still very much incurable. This is because it is difficult to change the SS genotype.
The only way to change the genotype of a person is through bone marrow transplant (BMT) or stem cell transplant. This procedure involves replacing the abnormal stem cell in the bone marrow of the sickle cell patient with the one of a healthy donor, especially a close relative like brother or sister.
However, this procedure posses high risks to the patients and are rarely performed. The main risk is graft versus host disease, where the transplanted cells attack normal cells in the body. It is a life-threatening reaction.