User:Kitana3678/sandbox

Sickle cell anaemia is a genetic disease caused by mutation in the gene that codes for haemoglobin production. The normal allele HbA, codes for normal haemoglobin. The mutant allele HbS, codes for an allele that produces a faulty type of haemoglobin.

The mutant allele Hbs has a tiny difference in the DNA base sequence and this changes the amino acid sequence in the haemoglobin, preventing the haemoglobin working as it should. This faulty haemoglobin has a tendency to produce fibres when the oxygen concentration is low, causing the red blood cells to get pulled into a sickle shape.

The two alleles are codominant.

A person with genotype HbA HbA has normal haemoglobin.

A person with genotype HbA HbS has a mix of normal and sickle cell haemoglobin.

And a person with genotype HbS HbS has all sickle cell haemoglobin.

The symptoms:

1) sickle cell crisis - happens when the red blood cells get pulled into a sickle shape and gets stuck in between blood capillaries. Due to fibres being produced by the faulty haemoglobin when oxygen concentraion is low

2) episodes of pain- pain is caused when an individual is under sickle cell crisis because of the blockages in the blood vessels that stop blood from flowing to some parts of the body.

3) Anaemia - anaemia is a common symptom among the individiuals with sickle cell anaemia due to a lack of red blood cells. sickle cells break apart easily and die leaving you with few blood cells.

4) fatigue - caused by poor oxgygen distribution to body cells which results in cells respiring less, releasing less energy.

Sickle cell Anaemia and Malaria.

A person who lives in a part of the world where malaria is present and who has some resistance to the disease, will be at advantage compared to others who are susceptible. Malaria is common in many parts of the world where the sickle cell allele is present in the population. People homozygous for sickle cell allele die early from sickle cell disease. And people who are homozygous for the normal allele often die early from malaria. However, people who are heterozygous for sickle cell are more resistant to malaria than those with all normal haemoglobin.

(HbA HbA - homozygous for the normal haemoglobin allele) - no sickle cell haemoglobin present. - not resistant to Malaria.

(HbS HbS - homozygous for the sickle cell allele) - all haemoglobin present are sickle cells.- not resistant to malaria.

(HbA HbS - heterozygous for the sickle cell allele) - some sickle cell haemoglobin is present. - resistant to malaria.