Q.Silencing of a gene could be achieved through the use of:

The question tests your understanding of how gene silencing works at the molecular level. Both RNA interference (RNAi) and antisense RNA technology are methods used to block the expression of a specific gene, though they operate through slightly different mechanisms.

RNAi involves introducing double-stranded RNA that is processed into small interfering RNAs (siRNAs), which then guide the degradation of complementary mRNA. Antisense RNA, on the other hand, is a single-stranded RNA molecule that binds directly to the target mRNA, preventing its …

The question asks about methods to silence a gene — that is, to prevent it from being expressed into a functional protein. In molecular biology, gene silencing is a powerful tool, both for studying gene function and for practical applications like creating pest-resistant plants. The NCERT textbook discusses two distinct but related approaches: RNA interference (RNAi) and antisense RNA technology.

Let us first understand the context. The NCERT Class 12 Biology textbook introduces RNAi in the chapter on Biotechnology and its Applications, specifically while explaining how transgenic plants like Bt cotton are made resistant to insect pests. The example given is of a nematode (a roundworm) that infects the roots of tobacco plants. Scientists wanted to silence a specific gene in the nematode so that it could not survive on the plant. They achieved this by introducing into the tobacco plant a DNA sequence that produced double-stranded RNA (dsRNA) complementary to the nematode's target gene. This dsRNA triggered RNAi in the nematode, effectively silencing that gene and making the plant resistant.

RNA interference works through a natural cellular mechanism. When double-stranded RNA enters a cell, an enzyme called Dicer cuts it into small fragments called small interfering RNAs (siRNAs). These siRNAs then bind to a protein complex called RISC, which uses one strand of the siRNA as a guide to find and destroy any messenger RNA (mRNA) that has a complementary sequence. Since mRNA is the template for protein synthesis, destroying it silences the gene. This is a highly specific and efficient process.

Antisense RNA technology is a related but slightly different approach. Here, a single-stranded RNA molecule is designed to be complementary to the target mRNA. This antisense RNA is introduced into the cell, where it binds to the sense mRNA (the normal message) by base pairing. The resulting double-stranded RNA molecule is then either degraded by cellular enzymes or physically blocks the ribosome from translating the mRNA into protein. The NCERT textbook mentions antisense RNA in the context of gene silencing, particularly in the chapter on Molecular Basis of Inheritance, where it is described as a method to prevent the expression of a gene. …

Method — check whether each mechanism can independently silence a gene

RNAi: yes, via dsRNA → siRNA → mRNA degradation (a distinct pathway).

Antisense RNA: yes, via a single ssRNA directly base-pairing with the target mRNA to block translation (a DIFFERENT, independent pathway). …