Sickle-cell anemia is a genetic disorder in which red blood cells take on an abnormal crescent shape. people who do not have sickle-cell anemia possess the following nucleotide and amino acid sequences: ctg act cct gag gag aag tct leu thr pro glu glu lys ser people who do have sickle-cell anemia possess the following nucleotide and amino acid sequences: ctg act cct gtg gag aag tct leu thr pro val glu lys ser sickle-cell anemia is an example of -- a. crossing-over. b. a gene mutation. c. nondisjunction. d. a chromosomal mutation.