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NEET NEET SOLVED PAPER 2015 (C)

  • question_answer
    In sea urchin DNA, which is double stranded 17% of the bases were shown to be cytosine.                                          The percentages of the other three bases expected to be present in this DNA are

    A)  G/34%, A/24.5%, T/24.5%

    B)  G/17%, A/16.5%, T/32.5%

    C)  G/17%, A/33%, T/33%

    D)  G/8.5%, A/50%, T/24.5%

    Correct Answer: C

    Solution :

    Chargaffs rule states that purine and pyrimidine base paires are present in equal amount, i.e. A = T, G = C. (A + T) = (G + C) \[\therefore \]                  \[\frac{A+T}{G+C}=1\] Cytosine = 17% If \[A+G+C+T=100\]and \[G=C,\,\,\,A=T\]Then \[A+17+7+T=100\] \[\therefore \] \[G=17%\] \[A+T+34=100\] \[A+T=100-34\] \[A+T=66\] \[A=T=33%=66\] Hence, if cytosine is 17%, then G = 17% A and T will be 33% each.


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