Ans. (A). Controlled at transcription.
Gene expression can be defined as a process, which involves synthesis of a final gene product by using information found in a gene. Regulation of gene expression, either to increase or decrease the synthesis of these gene products, is known as gene expression control and can be done at various levels.
Transcription includes formation of RNA molecule from a template DNA strand. Therefore, if gene expression is controlled during RNA synthesis, it is known as controlled at transcription.
Thus, the correct answer to be filled in the blank is option (A).
