Final answer:
If a cell's splicesomes were mutated so they no longer functioned normally, the likely outcome would be impaired mRNA processing. This can result in the synthesis of non-functional or abnormal proteins.
Step-by-step explanation:
If a cell's splicesomes were mutated so they no longer functioned normally, the likely outcome would be impaired mRNA processing (option C). Splicesomes are responsible for removing introns from pre-mRNA molecules during the process of mRNA maturation. Without functional splicesomes, introns would not be properly removed, leading to the production of mRNA with non-coding regions. This can result in the synthesis of non-functional or abnormal proteins.