Final answer:
The 'one gene-one polypeptide' theory states that a single gene codes for a single polypeptide chain. While some genes may encode for other types of RNA, the basic principle remains true. This concept has been significant in the field of molecular genetics.
Step-by-step explanation:
The 'one gene-one polypeptide' theory states that a single gene is responsible for producing a single polypeptide chain, which is a chain of amino acids that make up a protein. This theory was revised to the 'one gene-one polypeptide' hypothesis due to the discovery that some genes encode for transfer RNAs (tRNAs) or ribosomal RNAs (rRNAs) instead of polypeptides. However, the general principle holds true that genes code for specific polypeptides, and this concept has formed the basis for modern molecular genetics.