What is the HbS allele?

The HbS allele causes red blood cells to “sickle” instead of forming donut shapes from the HbA version. People with sickle cell trait have some of both. ( Wikimedia Commons) Sometimes carrying a “problem” allele is an advantage—people with the HbS allele are more resistant to malaria! ( Wikimedia Commons)

What causes the HbS allele?

HbS arises from a mutation substituting thymine for adenine in the sixth codon of the beta-chain gene, GAG to GTG. This causes coding of valine instead of glutamate in position 6 of the Hb beta chain. The resulting Hb has the physical properties of forming polymers under deoxy conditions.

What is the sickle cell allele?

The sickle cell anemia trait is found on a recessive allele of the hemoglobin gene. This means that you must have two copies of the recessive allele — one from your mother and one from your father — to have the condition. People who have one dominant and one recessive copy of the allele won’t have sickle cell anemia.

What type of mutation is HbS allele?

Sickle cell trait is caused by abnormal hemoglobin called sickle hemoglobin or Hb S. Sickle hemoglobin is as a result of a point mutation in the beta globin chain. This point mutation replaces A with T at codon 6 of beta hemoglobin chain. This causes the switch from glutamic acid to valine amino acid.

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What blood type carries sickle cell?

It is an inherited condition in which both hemoglobin A and S are produced in the red blood cells, always more A than S. Individuals with sickle cell trait are generally healthy.

How long can a person live with sickle cell disease?

With a national median life expectancy of 42–47 years, people with sickle cell disease (SCD) face many challenges, including severe pain episodes, stroke, and organ damage.

Is sickle cell curable?

Stem cell or bone marrow transplants are the only cure for sickle cell disease, but they’re not done very often because of the significant risks involved. Stem cells are special cells produced by bone marrow, a spongy tissue found in the centre of some bones. They can turn into different types of blood cells.

Why is sickle cell more common in Africa?

The sickle hemoglobin mutation reached polymorphic frequency in areas of Africa—other origins of the HbS gene were in the Middle East and Indian subcontinent—where malaria was prevalent, as carriers have a survival advantage and are more likely to survive to reproduce.

How many alleles are in a gene?

An allele is one of two or more versions of a gene. An individual inherits two alleles for each gene, one from each parent. If the two alleles are the same, the individual is homozygous for that gene.

How can a child have sickle cell anemia if neither parent has it?

Your child would have to inherit two sickle cell genes to have sickle cell disease. So if your child’s father does not have the sickle cell gene, your child can’t get sickle cell disease. But if your child’s father has the sickle cell gene, your child can get sickle cell disease.

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