Write a note on gene expression.

Hint: Gene expression is summarized in the Central Dogma which is first formulated by Francis Crick in 1958.

Complete answer: Gene expression is the process by which information from a gene is used in the synthesis of a functional gene product. These products are often proteins, but in non-protein-coding genes such as transfer RNA (tRNA) or small nuclear RNA (snRNA) genes, the product is a functional RNA.
1. The process of gene expression is used by all known life—eukaryotes, prokaryotes, and utilized by viruses—to generate the macromolecular machinery for life.
2. All steps in the gene expression process may be regulated, including the transcription, RNA splicing, translation, and post-translational modification of a protein.
3. The production of an RNA copy from a DNA strand is called transcription and is performed by RNA polymerases, which add one ribonucleotide at a time to a growing RNA strand as per the complementarity law of the nucleotide bases.
4. The translation is the production of RNA to protein.
5. Regulation of gene expression refers to the control of the amount and timing of the appearance of the functional product of a gene.

According to Central Dogma,

DNA → RNA → Protein
(transcription) (translation)

DNA can undergo replication to form DNA and transcription to form RNA.
RNA can undergo replication to form RNA and translation to form the protein.

Note: In some special cells, RNA synthesizes DNA, DNA synthesizes proteins. This process is known as RNA directed DNA synthesis.