Final answer:
If UG tries to occupy U1 without context referring to genetic code, and repeated trials fail, Solution II may retire the CCA codon from the proteome, hence avoiding detrimental effects except through random mutations, which are subject to tolerance and natural selection.
Step-by-step explanation:
When describing what happens to U1 after UG tries to occupy it in the context of genetic code reassignment, it is important to understand that U1 is likely a molecular constituent involved in genetic coding or translation processes. However, the student question does not provide sufficient context to identify exactly what U1 and UG are. Assuming U1 refers to a component of the genetic translation machinery, such as a tRNA or codon, and UG refers to an event where a codon is being reassigned or a tRNA is competing for a codon, the specific outcome would depend on the mechanism of genetic code expansion or reassignment in an organism.
It is mentioned that if repeated trials fail to reassign the CCA codon to a novel amino acid (NCAA), an alternative strategy could be employed by completely removing the CCA codon from the organism's proteome and deleting all tRNA(Pro)s that read this codon. This process would retire the CCA codon, turning it from an unassigned codon to an absent one, thus avoiding potential damage except when the codon reappears through random point mutations. These random mutations would be subject to the normal processes of cellular tolerance and natural selection, thus limiting their impact on the genome.
The information regarding "Keeping U due to its being the base most used for modifications", suggests that U1 may be retained in a genetic system for its potential roles which could be related to the stability of genetic code alterations and the adaptability of the organism.