What does gene expression refer to?

Gene expression refers to the synthesis of functional gene products, which primarily includes the production of proteins. This process involves transcribing DNA into messenger RNA (mRNA) and subsequently translating that mRNA into a specific protein. The regulation of gene expression is crucial for cellular function, as it determines which proteins are produced in a cell at any given time, influencing the cell's structure and function.

In contrast, the other choices represent different biological processes that do not directly relate to the concept of gene expression. For instance, the replication of DNA is focused on duplicating genetic material for cell division, not the expression of genes. Protein folding pertains to the post-translational modifications and proper structural formation of proteins after they are synthesized, rather than the initial expression of genes. The transfer of genetic material generally refers to processes such as genetic recombination or horizontal gene transfer, which do not involve the expression of a specific gene into its functional product. Therefore, the synthesis of functional gene products clearly encapsulates the essence of gene expression.