0 or 1 of previous expression; also forces minimal matching when an expression might match several strings within a search string. \. Preceding one of the above, it makes it a literal instead of a special character. Preceding a special matching character, see below.
sickle cell disease. Sickle cell anemia, a common form of sickle cell disease, is caused by a particular mutation in the HBB gene. This mutation results in the production of an abnormal version of beta-globin called hemoglobin S or HbS. In this condition, hemoglobin S replaces both beta-globin subunits in hemoglobin.
The mutation that causes sickle cell disease. A. occurs in the same gene that, when mutant in a different way, causes beta thalassemia. B. deletes two contiguous DNA bases. C. results in a single DNA base change that does not alter the encoded amino acid. D. changes a valine to a glutamic acid in the beta globin gene.