there are 61 mrna codons that specify an amino acid, but only 45 trnas. this is best explained by the fact that:

The specific department of health and human services (hhs) regulations that apply to research with children are known as: subpart b: additional protections for children involved as subjects in researchsubpart a: the common rulesubpart d: additional protections for children involved as subjects in researchsubpart c: protections for children in research