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Sickle cell anemia ( hemoglobin S disease ) : It is the most common of the red cell sicking diseases,is a genetic of the blood caused by a single nucleotide alteration in the beta-globin. A molecule of Hb S contains two normal alpha chains and two mutant beta-globin chains, in which glutamate at position six has been replaced with valine. Sickle cell anemia is a homozygous, recessive disorder. It is characterized by lifelong episodes of pain,chronic hemolytic anemia with associated hyperbilirubinemia and increased susceptibility to infection Heterozygotes contain both Hb S and Hb A.These individuals have sickle trait. They usually do not show clinical symptoms and can have normal lifespan. RFLP analysis:It is a diagnostic techniques for analyzing fetal DNA,rather than fetal blood,early detection of sickle cell anemia as well as other diseases. REF :Lippincott's textbook of biochemistry; 8th edition ;Page no :35,36 and 477.