6. Sickle cell anemia (disease) is described as an autosomal recessive condition

Question

6. Sickle cell anemia (disease) is described as an autosomal recessive condition (individuals must have two copies of the recessive allele to display “sickle cell disease”). However, sickle cell trait (the heterozygous condition) has a unique phenotype.

a. How would you classify/describe sickle cell trait at the organismal level (complete, incomplete, or co-dominance)? Explain your reasoning.

b. How would you classify/describe sickle cell trait at the molecular level (complete, incomplete, or co-dominance)? Explain your reasoning. (HINT: think about the hemoglobin lab)! Blood Phenotype Proteins on RBCs Possible Genotypes A type A IAIA or IAi B type B IBIB or IBi AB type A and type B IAIB O no A, no B ii

Explanation / Answer

a) At the organismal level, we can call sickle cell trait as co-dominance. In some cases some individuals have heterozygous condition (Ss), which carries both normal and sickle cell trait so they have mixture of red blood cells in their blood and survives normally, however, stressful condition can dominate the effect of sickle cell trait in these type of persons. Individuals who are double recessive (ss) suffers more as their will be more sickled shape red blood cells.

b) At the molecular level, we can call sickle cell trait as complete dominance. At the molecular level, in the protein chain of beta-globin of hemoglobin, at the sixth position glutamic acid gets replaced by valine and this type of mutation is known as single nucleotide polymorphism (SNP) which replaces one amino acid with the other. The result is the formation of sickle shape red blood cells which are unable to transport oxygen efficiently.

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