How is sickle cell anemia caused by genetic mutation?
Sickle cell disease (SCD) is a genetic disorder caused by a mutation in both copies of a person’s HBB gene. This gene encodes a component of hemoglobin, the oxygen-carrying protein in red blood cells. The mutation causes hemoglobin molecules to stick together, creating sickle-shaped red blood cells.
How was sickle cell created?
SCD originated in West Africa, where it has the highest prevalence. It is also present to a lesser extent in India and the Mediterranean region. DNA polymorphism of the beta S gene suggests that it arose from five separate mutations: four in Africa and one in India and the Middle East.
What type of genetic disorder is sickle cell anemia?
This condition is inherited in an autosomal recessive pattern , which means both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.
What mutation created 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.
Why does sickle cell trait exist?
In sickle cell anemia, the abnormal hemoglobin causes red blood cells to become rigid, sticky and misshapen. Both mother and father must pass the defective form of the gene for a child to be affected. If only one parent passes the sickle cell gene to the child, that child will have the sickle cell trait.
Why does sickle cell persist in human population?
The harmful alleles get eliminated from population over a period of time yet sickle cell anaemia is persisting in human population because SCA is a harmful condition which is also a potential saviour from malaria. Those with the benign sickle trait possess a resistance to malarial infection.
How is Huntington’s disease inherited?
Autosomal dominant inheritance pattern Huntington’s disease is caused by an inherited defect in a single gene. Huntington’s disease is an autosomal dominant disorder, which means that a person needs only one copy of the defective gene to develop the disorder.
Is HbS a gene or allele?
The HBB gene can come in at least two versions (or alleles): HbA and HbS. The HbA allele causes no problems but the HbS version can lead to either sickle cell trait or to the more severe sickle cell disease.
Is HbS allele recessive?
Inherited autosomal recessively, either two copies of Hb S or one copy of Hb S plus another beta-globin variant (such as Hb C) are required for disease expression.