What is defined as a section of DNA that carries the blueprint for making a protein?

The term that describes a section of DNA carrying the blueprint for making a protein is a gene. Genes are segments of DNA located on chromosomes and contain the necessary information for the synthesis of proteins, which are essential for the structure, function, and regulation of the body's cells, tissues, and organs.

Each gene is composed of sequences of nucleotides, which provide the instructions needed to build specific proteins. The process begins with transcription, where the gene is copied into messenger RNA, followed by translation, where ribosomes read this RNA to assemble amino acids into proteins.

The other terms presented relate to genetics and DNA but do not specifically refer to the sections of DNA coding for proteins. Chromosomes are structures composed of DNA that contain multiple genes. Codons are the specific sequences of three nucleotides in mRNA that correspond to particular amino acids during protein synthesis. Alleles are diverse forms of the same gene that can result in different traits. Thus, the definition of a gene is what makes it the correct answer to this question.