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Biology · 2026 · 5 marks
Biotechnology : Principles and ProcessesProcesses of Recombinant DNA Technology5 marksUnderstandlong answer
CBSE 2026 · Region 4 · Set 1 · Q33
(a) (i) EcoR I has played a very important role in rDNA technology. (I) Explain the convention for naming EcoR I. (II) Write the recognition site of…
(a)(i)
EcoR I has played a very important role in rDNA technology.
(I)
Explain the convention for naming EcoR I.
(II)
Write the recognition site of this endonuclease restriction enzyme.
(ii)
Name the overhanging stretches of DNA produced by these restriction enzymes. Describe their role in the formation of rDNA.
OR
(b)(i)
Insertional inactivation is a method to detect the recombinant DNA. Explain this method.
(ii)
Name the commonly used vector for transferring genes in plants from bacteria.
(iii)
How is this able to transform a normal plant cell into a tumour ?
Marking-scheme solution
(a)(i)
(I)
Naming of restriction enzymes (EcoRI):
-First letter ‘E’ of the name comes from genes (Escherichia)
The second two letters ‘co’come from the species (coli)
-The letter ‘R’ derived from the name of the strain
Roman number ($\displaystyle 1$) indicate the order in which the enzymes were isolated from the
strain of the bacteria.
(II)
The restriction enzyme EcoRI recognised the palindromic sequence
$\displaystyle 5$′ – G↓AATTC – $\displaystyle 3$′
$\displaystyle 3$′ – CTTAA↑G – $\displaystyle 5$′
(ii)
• These overhanging stretches are called ‘Sticky ends’
• They form hydrogen bond with their complementary cut counterpart that
facilitates the action of enzyme DNA ligase.
(i)
When the alien DNA is inserted within the coding sequence of the enzyme β -
galactosidase it results in inactivation of the enzyme which is referred as insertional inactivation.
The presence of chromogenic substrate gives blue coloured colonies if the plasmid
in the bacteria does not have insert or is non recombinant.
Colonies which do not produce any colour are identified as recombinants as their
gene for enzyme is inactivated due to an insert.
(ii)
Agrobacterium tumefaciens.
(iii)
When this Agrobacterium infects a plant cell it delivers ‘T’-DNA or Ti tumor-
inducing plasmid into the plant cell and transforms it into a tumor cell.
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CBSE Class 12 Biology past-paper question from the 2026 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.