1. (2) Sickle-cell anemia is a hereditary blood disorder, characterized by red b
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1. (2) Sickle-cell anemia is a hereditary blood disorder, characterized by red blood cells that assume an abnormal, rigid (sickle) shape due to a mutation in the hemoglobin protein; this causes many problems and reduced life expectancy (see figure below). Interestingly, individuals who are heterozygous for the trait (Ss) have an advantage in survival in the areas of the world where sickle-cell anemia is most common. Explain this heterozygote advantage using information here e and in your own words explain how this might keep the levels of the sickle cell anemia allele high A Normal red blood cells Normal red blood cell (RBC) of RBC RBCs flow freely within blood vessel Normal hemoglobin B Abnormal, sickled, red blood cells (sickle cells) Sickle cells blood flow Cross-section of sickle Sticky sickle cells Abnormal form strands that cause sickle shapeExplanation / Answer
Sickle cell anemia is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. People with two copies of the sickle cell gene have the disease.
Sickle cell anemia can make life more difficult, particularly for a child, who will need to deal with delayed sexual maturity and stunted growth. You will need to avoid things that can cause a crisis, such as certain medication that restricts blood vessels, high altitudes, and strenuous exercise.
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.
Sickle cell disease is caused by a recessive allele of the haemoglobin gene. When two copies are present (i.e. it is homozygous), many red blood cells become sickle-shaped, leading to disease.
However, if only one copy of this allele is present (heterozygous, or "sickle cell trait"), the carrier does not display symptoms. Additionally, the single copy confers resistance to malaria - a disease most common in tropical regions (e.g. sub-Saharan Africa). So in these regions, people with sickle cell trait are more likely to survive and reproduce than those without.
This amounts to a selective advantage for the sickle cell allele.
If an individual has sickle cell trait, it means that he or she carries or has inherited a single copy of the gene that doesn't causes sickle cell disease. It is not a disease. In general, people with sickle cell trait enjoy normal life spans with no medical problems .
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