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A strict but broad definition is an absolute decrease in red blood cell mass, [59] however, a broader definition is a lowered ability of the blood to carry oxygen. [60] An operational definition is a decrease in whole-blood hemoglobin concentration of more than 2 standard deviations below the mean of an age- and sex-matched reference range. [61]
A single point mutation in this polypeptide chain, which is 147 amino acids long, results in the disease known as Sickle Cell Anemia. [18] Sickle-cell anemia is an autosomal recessive disorder that affects 1 in 500 African Americans, and is one of the most common blood disorders in the United States. [17]
A vaso-occlusive crisis is a common painful complication of sickle cell anemia in adolescents and adults. [1] [2] It is a form of sickle cell crisis.Sickle cell anemia – most common in those of African, Hispanic, and Mediterranean origin – leads to sickle cell crisis when the circulation of blood vessels is obstructed by sickled red blood cells, causing ischemic injuries.
In the most common variant of sickle-cell disease, the 20th nucleotide of the gene for the beta chain of hemoglobin is altered from the codon GAG to GTG. Thus, the 6th amino acid glutamic acid is substituted by valine—notated as an "E6V" mutation—and the protein is sufficiently altered to cause the sickle-cell disease. [5]
The test uses the principles of gel electrophoresis to separate out the various types of hemoglobin and is a type of native gel electrophoresis.After the sample has been treated to release the hemoglobin from the red cells, it is introduced into a porous gel (usually made of agarose or cellulose acetate) and subjected to an electrical field, most commonly in an alkaline medium.
Strength of natural selection plot as a function of age. The antagonistic pleiotropy hypothesis (APT) is a theory in evolutionary biology that suggests certain genes may confer beneficial effects early in an organism's life, enhancing reproductive success, while also causing detrimental effects later in life, contributing to the aging process.