What is a gene?

A gene is fundamentally defined as a unit of heredity that consists of a specific segment of DNA. This definition encompasses the essence of what genes are and their primary role in biology. Genes serve as the instructions for the synthesis of proteins, which are crucial for many functions within an organism. Each gene contains the information needed to produce a particular protein or set of proteins, contributing to traits and characteristics passed down from one generation to the next.

While some definitions may involve RNA, genes are intrinsically linked to DNA, from which RNA and, subsequently, proteins are synthesized through the processes of transcription and translation. This connection is vital for understanding molecular biology and genetics. In contrast, other options provided do not accurately capture the full scope or function of a gene, which is why option A stands out as the correct answer.