25. Sickle Cell and Evolution of PBS: Watch a Mutation Story http://www.pbs.org/

Question

25. Sickle Cell and Evolution of PBS: Watch a Mutation Story http://www.pbs.org/wgbh/evolution/library /01/2/L012_02.html Sickle cell anemia causes the affected individual's hemoglobin to be defective reducing its oxygen carrying capacity and causing the characteristic "sickle" shaped cells to clump together. The clumping may cause clots, strokes, heart attacks and severe joint pain. An individual with sickle cell trait, is heterozygous for sickle cell, and has about half normal and half abnormal hemoglobin. However, the heterozygous individuals manifest very few to none of the symptoms of affected homozygous individuals. Give the genotype of an individual that is homozygous non-sickler. -Give the genotype of an individual that is heterozygous for sickle cell.. Give the genotype of an individual with sickle cell anemia.

Explanation / Answer

Sickle cell anemia:

Sickle cell anemia is the disease caused by mutation in the globin gene. It is a single nucleotide substitution that changes the protein composition. This change in protein composition affects the shape of the haemoglobin to be in sickle shape. This affects the oxygen carrying capacity of the haemoglobin.

Wild haemoglobin – HbA:

Beta haemoglobin gene at 6th position CTC codes for Glutamic acid. 26th position – CTC codes for glutamic acid.

HbS – sickle cell anemia, common in Middle East south Asia:

Beta haemoglobin gene at 6th position CAC codes for valine 26th position – CTC codes for glutamic acid.

HbC – sickle cell anemia, common in West African population:

Beta haemoglobin gene at 6th position TTC codes for lysine 26th position – CTC codes for glutamic acid.

HbE – sickle cell anemia, common in south East Asia:

Beta haemoglobin 6th position CTC codes for Glutamic acid. 26th position – TTC codes for lysine.

Answer:

3 types of genotypes can be formed by the combination of A and S allele. A allele for normal and S allele for sickle cell.

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