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Biology · 2023 · 1 mark
CBSE 2023 · Region 3 · Set 1 · Q2
Given below is a list of steps Meselson and Stahl carried out in their experiment to prove that DNA replication is semi-conservative. Select the…
Given below is a list of steps Meselson and Stahl carried out in their experiment to prove that DNA replication is semi-conservative. Select the option that gives the correct sequence of steps followed by them.
(i)
Bacteria transferred to a $\displaystyle \mathrm{N}^{14}$ medium and sampled every $\displaystyle 20$ minutes.
(ii)
All bacteria contain hybrid DNA (N $\displaystyle { }^{14}$ DNA and $\displaystyle \mathrm{N}^{15} \mathrm{DNA}$ ).
(iii)
Bacteria grown in $\displaystyle \mathrm{N}^{15}$ medium for many generations.
(iv)
All bacteria contain $\displaystyle \mathrm{N}^{15}$ DNA.
(v)
Bacteria contain either all $\displaystyle \mathrm{N}^{14}$ DNA or all hybrid DNA.
Official answer
(C)
$$ (iii) $\displaystyle \rightarrow$ (iv) $\displaystyle \rightarrow$ (i) $\displaystyle \rightarrow$ (ii) $\displaystyle \rightarrow$ (v)
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CBSE Class 12 Biology past-paper question from the 2023 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.