Here's why:

* DNA to mRNA: During transcription, the DNA sequence is copied into mRNA. The base pairing rules are slightly different:

* Adenine (A) in DNA pairs with Uracil (U) in mRNA

* Thymine (T) in DNA pairs with Adenine (A) in mRNA

* Guanine (G) in DNA pairs with Cytosine (C) in mRNA

* Cytosine (C) in DNA pairs with Guanine (G) in mRNA

* TAC in DNA: The DNA codon TAC codes for the amino acid methionine (Met).

* AUG in mRNA: Since T pairs with A in mRNA, the mRNA codon corresponding to TAC is AUG.

Important Note: AUG is also the start codon, meaning it signals the beginning of protein synthesis.