Read the given paragraph carefully and answer the following questions:
Since the DNA is enclosed within the membranes, we have to break the cell open to release DNA along with other macromolecules such as RNA, proteins, polysaccharides and also lipids. This can be achieved by treating the bacterial cells/plant or animal tissue with enzymes such as lysozyme (bacteria), cellulase (plant cells), chitinase (fungus). There are some basic steps in genetically modifying an organism – (i) identification of DNA with desirable genes; (ii) introduction of the identified DNA into the host; (iii) maintenance of introduced DNA in the host and transfer of the DNA to its progeny. Agrobacterium tumifaciens, a pathogen of several dicot plants is able to deliver a piece of DNA known as 'T-DNA' to transform normal plant cells into a tumor and direct these tumor cells to produce the chemicals required by the pathogen. Other molecules can be removed by appropriate treatments and purified DNA ultimately precipitates out after the addition of chilled ethanol. Selection of recombinants due to inactivation of antibiotics is a cumbersome procedure because it requires simultaneous plating on two plates having different antibiotics. Therefore, alternative selectable markers have been developed which differentiate recombinants from non-recombinants on the basis of their ability to produce colour in the presence of a chromogenic substrate. In this, a recombinant DNA is inserted within the coding sequence of an enzyme, β-galactosidase. This results into inactivation of the gene for synthesis of this enzyme, which is referred to as insertional inactivation.
Which one of the following steps is not involved in genetic modification of an organism?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Identification of RNA
Genetic modification means moving a desired gene into an organism so that it gains a new trait. The gene is a piece of DNA, and the whole method handles DNA.
Option (1) Maintenance of introduced DNA in the host and Transfer of the DNA to its progeny — A step of genetic modification. It is the third step. The new DNA must stay in the host and pass to its offspring, or the trait is lost after one generation.
Option (2) Identification of DNA — A step of genetic modification. It is the first step. Scientists must first find the DNA carrying the desirable gene.
Option (3) Introduction of the identified DNA into the host — A step of genetic modification. It is the second step. The identified DNA is put into the host, often with a vector.
Option (4) Identification of RNA — Not a step of genetic modification. The gene that is moved is DNA, not RNA. RNA is in fact removed (with ribonuclease) when DNA is purified for this work.
Note: The passage is taken from NCERT. NTA has put lines of the NCERT text together to make it. Most CUET (UG) questions come straight from NCERT, so study the book line by line, including figures and their titles.