Sickel cell disease occurs when the body produces abnormal hemoglobin this is caused by a) duplication of a gene b) a sequence change in a single gene c) nondisjunction of a chromosome d) crossing over with in a chromosome

Sickle cell disease occurs when the body produces abnormal hemoglobin. This is caused by B) a sequence change in a single gene.
There is a DNA base pair change, a substitution called a point mutation, that leads to the wrongful addition of one single amino acid (Valine) to the growing hemoglobin protein where Glutamate normally would be. This one swap of an amino acid leads to all of the functional differences of the altered hemoglobin proteins and the red blood cells containing these, accounting for the features of the disease.

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