In squirrels and chipmunks, as in humans, cholesterol is removed from the circulation, first by complexing with Low Density Lipoproteins (LDLs). Next, the cholesterol-LDL complex is bound to LDL receptors found predominantly on the surface of liver cells, which then undergo receptor-mediated endocytosis, thus removing the LDL-cholesterol from the blood serum. Inside the cells, a drop in pH causes the LDLs to separate from their receptors, and the receptors are ultimately returned to the cell surface via exocytosis. You are surprised to discover that in both squirrels and chipmunks, certain individuals are predisposed to suffering heart attacks at an early age, and these early heart attacks are linked to the presence of a mutation in the gene that codes for their LDL receptors. This is where the similarity ends. Closer examination of the chipmunks suffering from elevated serum cholesterol levels reveals that many individuals that are homozygous for the Fa allele also have large, subcutaneous tumors present on their legs and buttocks, cholesterol deposits on their eyelids, a grey or blue ring around the edge of the cornea of the eye, and tendonitis. NAME and DEFINE the genetic phenomenon illustrated here.
In squirrels and chipmunks, as in humans, cholesterol is removed from the circulation, first by complexing with Low Density Lipoproteins (LDLs). Next, the cholesterol-LDL complex is bound to LDL receptors found predominantly on the surface of liver cells, which then undergo receptor-mediated endocytosis, thus removing the LDL-cholesterol from the blood serum. Inside the cells, a drop in pH causes the LDLs to separate from their receptors, and the receptors are ultimately returned to the cell surface via exocytosis.
You are surprised to discover that in both squirrels and chipmunks, certain individuals are predisposed to suffering heart attacks at an early age, and these early heart attacks are linked to the presence of a mutation in the gene that codes for their LDL receptors. This is where the similarity ends.
Closer examination of the chipmunks suffering from elevated serum cholesterol levels reveals that many individuals that are homozygous for the Fa allele also have large, subcutaneous tumors present on their legs and buttocks, cholesterol deposits on their eyelids, a grey or blue ring around the edge of the cornea of the eye, and tendonitis. NAME and DEFINE the genetic phenomenon illustrated here.
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