Final answer:
Genomic DNA (C) represents a complete copy of the genome and contains all the genetic information of an organism. Not all parts of the genome are always expressed, which differentiates it from mRNA, tRNA, or rRNA, which are involved in expressing and synthesizing proteins.
Step-by-step explanation:
The substance that represents a complete copy of the genome that might or might not be expressed is C) Genomic DNA. Unlike mRNA, tRNA, or rRNA, genomic DNA contains the entire genetic information required to specify the structure of all the proteins and RNAs of an organism. Genes consist of many elements such as mRNA, tRNA, rRNA, regulatory sequences, and more.
However, it is the genomic DNA that carries the full set of genetic instructions within a cell. It's the same in every cell of an organism, even though not all genes are expressed in every cell. mRNA, on the other hand, is a transcript of a particular gene or genes and represents the instructions for making specific proteins; its sequences match parts of the DNA, but it only includes the information that is currently being expressed to synthesize proteins.
tRNA and rRNA have distinct roles in protein synthesis, with tRNA carrying specific amino acids to the ribosome, and rRNA being part of the structure and machinery of ribosomes where proteins are made.