Question

Control of gene expression takes place at the level of:
A. DNA-replication
B. Transcription
C. Translation
D. None of the above

Answer 1

Gene expression is the process through which information from a gene is used to create a functioning gene product that allows it to make end products, such as protein or non-coding RNA, and, as a result, change phenotype. Protein-coding genes, like transfer RNA (tRNA) and small nuclear RNA (snRNA), produce proteins, whereas non-protein-coding genes, like transfer RNA (tRNA) and small nuclear RNA (snRNA), produce a functional non-coding RNA.

Complete answer :
Option A DNA replication : The biological process of making two identical DNA replicas from a single original DNA molecule is known as DNA replication. DNA replication is a necessary component of biological inheritance in all living organisms. The gene expression control does not take place at DNA replication level. Hence option A is not correct.
Option B Transcription : The process of converting a section of DNA to RNA is known as transcription. Messenger RNA is made up of segments of DNA that have been translated into RNA molecules that can encode proteins. The amount of mRNA produced by a gene is limited, which allows transcription to be controlled. Gene expression can be manipulated in this way. Hence option B is the correct answer.
Option C Translation : Translation is the process by which ribosomes in the cytoplasm or endoplasmic reticulum create proteins after DNA is converted to RNA in the nucleus. Entire process is known as gene expression. Only some control is achieved through translation. Hence option C is not correct.
Option D None of the above : Since option B is the correct answer, option D is wrong.

Hence, option B. Transcription is the correct answer.

Note :
Some viruses (such as HIV, the virus that causes AIDS) can convert RNA to DNA. The HIV genome is made up of RNA that is reverse transcribed into DNA. The resultant DNA can be fused with the host cell's DNA genome. Reverse transcriptase is the major enzyme involved in the creation of DNA from an RNA template. Reverse transcriptase is responsible for producing a complementary DNA strand (cDNA) to the viral RNA genome in the case of HIV.