In sea urchin DNA , which is double stranded, 17% of bases were shown to be cytosine.percentages of

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5.Molecular Basis of Inheritance

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

$G\ 17\%, A\ 33\%, T\ 33\%$

$G\ 8.5\%, A\ 50\%, T\ 24.5\%$

$G\ 34\%, A\ 24.5\%, T\ 24.5\%$

$G\ 17\%, A\ 16.5\%, T\ 32.5\%.$

(NEET-2015)

Solution

(a) : According to Chargaff’s rule, the amount of adenine is always equal to that of thymine and the amount of guanine is always equal to that of cytosine, $ i.e., A = T$ and $G = C$. Also, the purines and pyrimidines are always in equal amounts, $i.e., A + G = T + C$. Now, given ds $DNA$ has $17\%$ cytosine and hence guanine will be also $17\%$. So, $A + T$ must be $66\%$, therefore, percentage of adenine or thymine would be $66/2 = 33\%$.

Standard 12

Biology