What is the fundamental unit of inheritance that determines the amino acid sequence in polypeptides?

The fundamental unit of inheritance that determines the amino acid sequence in polypeptides is a gene. Genes are segments of DNA that contain the instructions for synthesizing proteins, which are made up of polypeptides. During the process of transcription, the information in a gene is transcribed into messenger RNA (mRNA), which then undergoes translation to build polypeptides. Each sequence of three nucleotides in the mRNA, known as a codon, corresponds to a specific amino acid. Therefore, the gene directly dictates the order of amino acids in a polypeptide chain, thereby determining the structure and function of proteins.

While chromosomes contain many genes and serve as the larger structural units of heredity, it is the gene itself that carries the specific information needed to produce a polypeptide. Amino acids are the building blocks of polypeptides but do not themselves carry genetic information. Polypeptides are the final product that results from the gene expression process, but they do not influence inheritance directly. Thus, a gene is the correct answer as it encompasses the necessary information for determining the amino acid sequence in proteins.