Which of the following is/are the basic step(s) in genetically modifying an organism? 1. Identification of DNA with desirable genes 2. Introduction of the identified DNA into the host 3. Maintenance of introduced DNA in the host and transfer of the DNA to its progeny Select the correct answer using the code given below.
- A.1 only
- B.1, 2 and 3
- C.2 and 3 only
- D.3 only
Correct answer
Explanation
The correct answer is B, 1, 2 and 3. Making a genetically modified organism needs all three steps: find the useful DNA, put it into the host, and make sure the host keeps it and passes it on.
Recombinant DNA technology works in this order. First the gene for the desired trait, such as insect resistance, is identified and cut out with restriction enzymes. Next it is joined to a vector, usually a plasmid or a virus, using DNA ligase, and introduced into the host cell. Finally the DNA must be maintained in the host and copied when the cell divides, so that the new trait is inherited by its progeny. Bt cotton, which carries a gene from the bacterium Bacillus thuringiensis, was made this way.
A is wrong because identifying the gene alone does not change the organism. C is wrong because a gene cannot be introduced before it is identified. D is wrong because maintenance has nothing to maintain without the first two steps.
Exam tip: restriction enzymes are the molecular scissors, DNA ligase the molecular glue, and plasmids the usual vectors.
Practice Questions
View allWhich of the following statements about a fluid at rest in a cup is/are correct? 1. Pressure is same at all the points in the fluid 2. Pressure is exerted on the walls. 3. Pressure exists everywhere in the fluid. Select the correct answer using the code given below :
- A.1 and 2 only
- B.2 and 3 only
- C.1 only
- D.1, 2 and 3
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A fluid at rest presses on the walls and has pressure at every point, but that pressure is not the same at all depths.
Read the full explanation →The absolute zero temperature is 0 Kelvin. In °C unit, which one of the following is the absolute zero temperature?
- A.0 °C
- B.-100 °C
- C.-273.15 °C
- D.-173.15 °C
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Zero on the Kelvin scale lies 273.15 degrees below the freezing point of water. The Kelvin and Celsius scales have degrees of the same size, so T(K) = t(°C) + 273.15.
Read the full explanation →Dinitrogen (N₂) and dioxygen (O₂) are the main constituents of air but they do not react with each other to form oxides of nitrogen because
- A.the reaction requires initiation by a catalyst
- B.oxides of nitrogen are unstable
- C.the reaction is endothermic and requires very high temperature
- D.the stoichiometry of N₂ and O₂ in air is not ideal for the reaction to take place
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Nitrogen and oxygen combine only when a lot of energy is supplied. The nitrogen molecule is held by a very strong triple bond, so breaking it takes much energy, and the reaction N₂ + O₂ → 2NO absorbs heat.
Read the full explanation →Hydrogenation of vegetable oils using nickel catalyst is an example of
- A.Substitution reaction.
- B.Elimination reaction.
- C.Addition reaction.
- D.Free-radical polymerization.
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Hydrogen adds across the carbon–carbon double bonds of the oil. Vegetable oils are unsaturated: their fatty acid chains contain C=C double bonds, which keep them liquid.
Read the full explanation →A positive charge is moving towards south in a space where magnetic field is pointing in the north direction. The moving charge will experience :
- A.a deflecting force towards north direction.
- B.a deflecting force towards east direction.
- C.a deflecting force towards west direction.
- D.no deflecting force.
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The charge moves exactly opposite to the field, and a magnetic field exerts no force on a charge moving along its line.
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