Final answer:
Preferred codons in mRNA during protein synthesis are determined by the most abundant tRNA molecules available to pair with the codons.
Step-by-step explanation:
Preferred codons are represented by the most abundant tRNA. The cellular process of transcription generates messenger RNA (mRNA), which is then used during translation to specify a sequence of amino acids forming a protein. The genetic code consists of 64 possible mRNA codons, which are read by tRNA molecules during protein synthesis. The abundance of specific tRNAs has a direct influence on which codons are preferably used for encoding a particular amino acid, as each tRNA has an anticodon that pairs with a corresponding mRNA codon. Some tRNAs can recognize more than one codon due to wobbling, which contributes to this preference.