The DNA segment that carries information for coding one protein or polypeptide is called a gene. According to one gene-one polypeptide hypothesis, each gene is responsible for making a single chain of the polypeptide.
Originally it was said that one gene codes for one enzyme but later it was found that some gene also codes for non-enzyme proteins and single polypeptide chains. So after this research, the theory was modified and one gene-one polypeptide theory came. Therefore the right answer is gene.
