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Zoology MCQs for NEET — Practice Questions with Answers

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In the context of detecting mutated genes, a radioactive probe is used. What characteristic of the probe is crucial for its detection using autoradiography?

A. Its ability to amplify the gene of interest. B. Its single-stranded nature and radioactivity. C. Its complementary binding to the mutated gene. D. Its ability to form antigen-antibody complexes.

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Explanation

The context mentions: 'A single stranded DNA or RNA, tagged with a radioactive molecule (probe) is allowed to hybridise to its complementary DNA in a clone of cells followed by detection using autoradiography.' The radioactivity is essential for detection via autoradiography.

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What is the basis of detection in ELISA?

A. Amplification of nucleic acids. B. Hybridization of radioactive probes. C. Antigen-antibody interaction. D. Separation of DNA fragments by electrophoresis.

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Explanation

The NCERT text clearly states: 'ELISA is based on the principle of antigen-antibody interaction. Infection by pathogen can be detected by the presence of antigens (proteins, glycoproteins, etc.) or by detecting the antibodies synthesised against the pathogen.'

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Why would a clone having a mutated gene NOT appear on a photographic film when using a radioactive probe and autoradiography for detection?

A. The mutated gene cannot be amplified by PCR. B. The probe will not have complementarity with the mutated gene. C. The mutated gene interferes with the radioactive tag. D. Autoradiography only detects healthy genes.

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Explanation

The NCERT text explains: 'The clone having the mutated gene will hence not appear on the photographic film, because the probe will not have complementarity with the mutated gene.'

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The three main steps in each cycle of Polymerase Chain Reaction (PCR) are:

A. Denaturation, Annealing, Extension B. Ligation, Restriction, Amplification C. Isolation, Hybridization, Detection D. Transcription, Translation, Replication

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Explanation

Figure 9.6 and its caption in the 'BIOTECHNOLOGY - PRINCIPLES AND PROCESSES' chapter explicitly state: 'Polymerase chain reaction (PCR) : Each cycle has three steps: (i) Denaturation; (ii) Primer annealing; and (iii) Extension of primers'.

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Which of the following is an advantage of using PCR for disease diagnosis?

A. It eliminates the need for expensive radioactive probes. B. It can detect very low concentrations of pathogens before symptoms appear. C. It directly detects antibodies produced against a pathogen. D. It can only be used for bacterial infections, not viral.

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Explanation

The context highlights: 'However, very low concentration of a bacteria or virus (at a time when the symptoms of the disease are not yet visible) can be detected by amplification of their nucleic acid by PCR.'

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How does PCR amplify a gene of interest?

A. By using restriction enzymes to cut out multiple copies. B. By synthesising multiple copies of the DNA in vitro. C. By incorporating the gene into a plasmid and growing the bacteria. D. By directly creating proteins from the DNA sequence.

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Explanation

The NCERT text states: 'In this reaction, multiple copies of the gene (or DNA) of interest is synthesised in vitro using two [primers]'. This refers to the core mechanism of PCR.

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To detect an infection by a pathogen using ELISA, what can be detected?

A. Only the nucleic acid of the pathogen. B. Only the antibodies synthesized against the pathogen. C. Either the antigens of the pathogen or the antibodies synthesized against it. D. The presence of mutated genes in the host.

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Explanation

The text states: 'Infection by pathogen can be detected by the presence of antigens (proteins, glycoproteins, etc.) or by detecting the antibodies synthesised against the pathogen.'

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Which of these diagnostic methods involves the amplification of nucleic acids?

A. ELISA B. Autoradiography (for probe detection) C. Polymerase Chain Reaction (PCR) D. Restriction enzyme digestion

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Explanation

The context specifically mentions: '...very low concentration of a bacteria or virus (at a time when the symptoms of the disease are not yet visible) can be detected by amplification of their nucleic acid by PCR.'

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What is the primary role of Recombinant DNA technology in molecular diagnostics, as suggested by the context?

A. To perform antigen-antibody interactions. B. To amplify specific DNA sequences directly. C. To serve as a technique for early diagnosis, often by enabling precise detection methods. D. To separate DNA fragments based on their charge.

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Explanation

The context groups Recombinant DNA technology with PCR and ELISA as 'some of the techniques that serve the purpose of early diagnosis.' While PCR involves amplification and ELISA involves antigen-antibody interactions, recombinant DNA technology encompasses broader genetic manipulation that can facilitate accurate diagnostics.

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If a healthy individual's DNA is probed with a radioactive single-stranded DNA sequence corresponding to a known pathogenic gene, and no signal is detected via autoradiography, what does this indicate?

A. The individual is producing antibodies against the pathogen. B. The individual does not possess the pathogenic gene. C. The pathogenic gene is present but not expressed. D. The probe used was not single-stranded.

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Explanation

The principle for detecting mutated genes using a probe is that 'the probe will not have complementarity with the mutated gene.' Conversely, if a probe for a pathogen gene is used and no hybridization occurs (thus no signal), it implies the complementary sequence (the pathogenic gene) is absent in the individual's DNA.

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