What is a gene?

A gene is defined as a specific sequence of DNA that contains the instructions needed to produce proteins. Proteins are essential molecules that play critical roles in the body, such as serving as enzymes, hormones, and structural components of cells and tissues. The gene's sequence is transcribed into messenger RNA (mRNA), which is then translated into a protein by ribosomes in the cytoplasm. This process is central to the functioning of all living organisms and is fundamental to how traits are inherited.

Other options, while related to molecular biology, do not accurately capture the complete definition of a gene. For example, the option mentioning RNA pertains to regulatory functions, but it does not describe the role of DNA sequences themselves. Moreover, the mention of small fragments of DNA and structures in the cytoplasm focuses on specific aspects of genetic processes but falls short of defining what a gene actually is in the context of heredity and protein synthesis. Thus, identifying a gene as a section of DNA carrying the blueprint for making a protein is the most accurate and encompassing description.