<prompt> Which of the following can be a homologous substitution for valine in hemoglobin?IsoleucineGlutamic acidPhenylalanineLysine  <response>: In Many examples of Point Mutations The classic example is sickle-cell disease, which is caused by mutation of a single base out of the 3 x 109 in the genome, a T-to-A DNA substitution, which in turn results in an A-to-U change in the mRNA corresponding to the sixth codon of the b-globin gene. The altered codon specifies a different amino acid valine rather than glutamic acid, and this causes a structural abnormality of the b-globin molecule leading to hemoglobin aggregation and red blood cell sickling. Ref: Harpers Illustrated Biochemistry, 30E 2015 Pg no 460. 