Biology Class 12 NCERT Solutions: Chapter 11 Biotechnology: Principles and Processes Part 3

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Q.8 Can you recall meiosis and indicate at what stage a recombinant DNA is made?


  • Meiosis is a process that includes the reduction in the amount of genetic material. It is of two types, namely meiosis I and meiosis II.

  • During the pachytene stage of prophase l, crossing over of chromosomes takes place where the exchange of segments between non-sister chromatids of homologous chromosomes takes place.

  • This results in the formation of recombinant DNA.

Image of Meiosis

Image of Meiosis

Q.9 Can you think and answer how a reporter enzyme can be used to monitor transformation of host cells by foreign DNA in addition to a selectable marker?


  • A reporter gene can be used to monitor the transformation of host cells by foreign DNA.

  • They act as a selectable marker to determine whether the host cell has taken up the foreign DNA or the foreign gene gets expressed in the cell.

  • The researchers place the reporter gene and the foreign gene in the same DNA construct.

  • Then, this combined DNA construct is inserted in the cell then, the reporter gene is used as a selectable marker to find out the successful uptake of genes of interest.

  • Example of reporter genes - lac Z gene, which encodes a green fluorescent protein in a jelly fish.

Q.10 Describe briefly the following:

(a) Origin of replication

(b) Bioreactors

(c) Downstream processing


(a) Origin of replication:

  • Origin of replication is defined as the DNA sequence in a genome from where replication initiates.

  • The initiation of replication can be either uni-directional or bi- directional.

  • A protein complex recognizes the ‘on’ site unwinds the two strands, and initiates the copying of the DNA.

(b) Bioreactors:

  • Bioreactors are large vessels used for the large-scale production of biotechnology products from raw materials.

  • They provide optimal conditions to obtain the desired product by providing the optimum temperature, pH, vitamin, oxygen, etc.

  • Bioreactors have an oxygen delivery system a foam control system a PH, a temperature control system, and a sampling port to obtain a small volume of culture for sampling.

(c) Downstream processing:

  • Downstream processing is a method of separation and purification of foreign gene products after the completion of the biosynthetic stage.

  • The product is subjected to various processes in order to separate and purify the product.

  • After downstream processing, the product is formulated and is passed through various clinical trials for quality control and other tests.

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