Answer:
C) A changed to G in the first position of the codon.
Explanation:
In the translation of DNA, triplets or codons of mRNA (a group of three nucleotides) are read according to a genetic code, to build proteins.
Proteins are composed of amino acids. In the translation process, each codon codes for an particular amino acid according to the genetic code as illustrated in the DNA codon table (attached here).
In this table we can see that if the first position of any of the codons coding for Threonine ( ACT, ACC, ACA, ACG) is changed for G, Adenine is going to be encoded instead of threonine.
