Final answer:
Segments of polypeptides that remain after protein splicing are called exons, which are spliced together to form the final mRNA for protein synthesis.
Step-by-step explanation:
Segments of polypeptides that are retained following protein splicing are known as exons. Protein splicing is a process that involves the removal of non-coding sequences, termed introns, from the pre-mRNA. The exons, which are the coding sequences, are spliced together to form a continuous sequence that codes for a functional polypeptide. Following this process, the mRNA is then translated into a polypeptide, which may undergo further modifications to become a fully functional protein. Notably, in some cases, through alternative splicing, different sets of exons can be joined in various combinations, leading to the production of multiple polypeptide variants from a single gene.