The β chain of adult hemoglobin is composed of 146 amino acids of a known sequence. In comparing the normal β chain with the β chain in sickle-cell hemoglobin, what alteration is one likely to find?
◦ glutamic acid replacing valine in the first position
◦ valine instead of glutamic acid in the sixth position
◦ trinucleotide repeats
◦ extensive amino acid substitutions
◦ frameshift substitutions