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Biology · 2025 · 3 marks
CBSE 2025 · Region 7 · Set 2 · Q24
The base sequence in one of the strands of DNA is: 'TAGCATGAT' (a) Give the base sequence of its complementary strand. (b) How are these base pairs…
The base sequence in one of the strands of DNA is : 'TAGCATGAT'
(a)
Give the base sequence of its complementary strand.
(b)
How are these base pairs held together in DNA molecule ?
(c)
Explain the base complementarity rule. Name the scientist who framed this rule.
Marking-scheme solution
(a)
‘A T C G T A C T A’
(b)
Base pairs are held by weak hydrogen bonds/ A pairs with T with two H-
bonds and G pairs with C forming three H-bonds
(c)
• In a double-stranded DNA the ratios between Adenine and Thymine
and Guanine and Cytosine are constant and equal to one .
• Erwin Chargaff
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CBSE Class 12 Biology past-paper question from the 2025 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.