Q178 / 200 · NEET 2022 (Phase 2) · Zoology

If $A$ and $C$ make $30 \%$ and $20 \%$ of DNA, respectively, what will be the percentage composition of $\mathrm{T}$ and $\mathrm{G}$ ?

  • A
    $\mathrm{T}: 20 \%, \mathrm{G}: 30 \%$
  • Correct answer
    B
    $\mathrm{T}: 30 \%, \mathrm{G}: 20 \%$
  • C
    $\mathrm{T}: 30 \%, \mathrm{G}: 30 \%$
  • D
    $\mathrm{T}: 20 \%, \mathrm{G}: 20 \%$

Solution

$$ \begin{aligned} & \mathrm{A} \rightarrow 30 \%=\mathrm{T} \rightarrow 30 \% \\ & \mathrm{C} \rightarrow 20 \%=\mathrm{G} \rightarrow 20 \% \end{aligned} $$ According to chargaff's rule, Adenine (A) pairs with Thymine (T) and Cytosine (C) pairs with Guanine (G). So, The ds DNA have equal percentage of $A$ and $T$ or $G$ and $C$.

Hence, the correct answer is option: 'B'.

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