Zoology MCQs for NEET — Practice Questions with Answers

The NCERT text explicitly states, 'Recombinant DNA can then be forced into such cells by incubating the cells with recombinant DNA on ice, followed by placing them briefly at 42°C (heat shock), and then putting them back on ice. This enables the bacteria to take up the recombinant DNA.' This protocol renders the cells competent.

The context clearly states, 'Most likely, this piece of DNA would not be able to multiply itself in the progeny cells of the organism. But, when it gets integrated into the genome of the recipient, it may multiply and be inherited along with the host DNA. This is because the alien piece of DNA has become part of a chromosome, which has the ability to replicate. In a chromosome there is a specific DNA sequence called the origin of replication, which is responsible for initiating replication.'

The NCERT states, '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.'

The text mentions, 'Recipient cells after making them ‘competent’ to receive, take up DNA present in its surrounding.' The entire process of physical and chemical treatment aims to make the cell membrane permeable to foreign DNA.

The NCERT text states, 'In a method known as micro-injection, recombinant DNA is directly injected into the nucleus of an animal cell.' Gene gun is suitable for plants, Agrobacterium for plants, and heat shock/chilling primarily for bacteria.

The NCERT mentions, 'In another method, suitable for plants, cells are bombarded with high velocity micro-particles of gold or tungsten coated with DNA in a method known as biolistics or gene gun.'

The text states, 'In a chromosome there is a specific DNA sequence called the origin of replication, which is responsible for initiating replication. Therefore, for the multiplication of any alien piece of DNA in an organism, it needs to be integrated...'

The NCERT states, 'Similarly, retroviruses in animals have the ability to transform normal cells into cancerous cells. A better understanding of the art of delivering genes by pathogens in their eukaryotic hosts has generated knowledge to transform these tools of pathogens into useful vectors for delivering genes of interest to humans.'

While competence can refer to various cells, the most direct and common method described for making host cells (specifically referring to 'Recipient cells after making them ‘competent’ to receive, take up DNA present in its surrounding') is in the context of bacterial transformation using heat shock/chilling protocol for plasmid uptake. The subsequent example given is 'if a recombinant DNA bearing gene for resistance to an antibiotic (e.g., ampicillin) is transferred into E. coli cells...'

The NCERT explains, 'If we spread the transformed cells on agar plates containing ampicillin, only transformants will grow, untransformed recipient cells will die.' This principle is used for selection, where the ampicillin resistance gene acts as a selectable marker.