The sickle-cell mutation involves a single base change from normal hemoglobin (Slide 8). What is the significance of this mutation? a. It switches the order of leucine, threonine, and proline in the amino acid sequence. b. It puts valine in the amino acid chain instead of glutamic acid, resulting in an abnormal protein. c. It inserts a new “start” codon methionine where the serine amino acid should be. d. It places a “stop” codon too early in the amino acid chain.