Final answer:
The substitution of alanine for threonine at amino acid position 229 may have resulted from a missense mutation, in which a different codon sequence codes for a different amino acid. One possible change is the substitution of the threonine codon ACG to GCG, resulting in serine-valine-threonine-tyrosine.
Step-by-step explanation:
A missense mutation occurs when there is a substitution of one nucleotide in a codon, resulting in the incorporation of a different amino acid in the protein. In this case, the substitution of alanine for threonine at amino acid position 229 suggests a change in the codon sequence for that position.
Let's assume the original codon sequence was AUG-AAU-ACG-GCU, which codes for methionine-asparagine-threonine-alanine. To predict the change that led to the substitution, we can compare it to different codon sequences resulting in alanine at position 229.
One possible scenario is a missense mutation caused by the substitution of the threonine codon ACG to GCG, resulting in AGC-GCG-ACC-TAC. This sequence would code for serine-valine-threonine-tyrosine, which shows that the original threonine has been replaced by alanine.