Why does sickle-cell hemoglobin (hbs) migrate slower than normal hemoglobin (hba) during gel electrophoresis?

The cause a translocation of the amino acid in position of a normal beta globin, transforming glutamic acid into valine. Then the HBs has less charge due to loss of the glutamic acid.Sickle-cell anemia is a hereditary disease make  by hemoglobin S in its homozygous form. 

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lizards have adapted to life in the desert. some desert lizards have toes with spiny scales to them run across the sand without sinking. some use the sand to hide from predators, or to search for small animals that they prey upon.