Directions : In the following question more than one of the answers given may be correct. Select the correct answer and mark it according to the code:
In case of double-stranded DNA, which of die following base ratios are equal to one ? (1) \[\text{(G+T)}\,\text{/(A}\,\text{+C)}\] (2) \[\text{(A+G)}\,\text{/(C}\,\text{+T)}\] (3) \[C\,\text{/G}\,\] (4) \[\text{(A+T)}\,\text{/(G}\,\text{+C)}\]A) 1, 2 and 3 are correct
B) 1 and 2 are correct
C) 2 and 4 are correct
D) 1 and 3 are correct
Correct Answer: A
Solution :
Chargaff (1950) discovered the equivalence rule, which suggested that despite wide compositional variations exhibited by different types of DNA, the total amount of purines equals to the amount of pyrimidine \[(A+G=T+C).\]The amount of adenine equals to the amount of thymine \[A=T).\]and the amount of guanine equals to the amount of cyrosin \[G=C).\] In contrast, the \[(T+A/G+C).\] ratio varied widely in DNAs of different species. In case of double-stranded \[(A+G)/(C+T)\,C/G\]and \[(G+T)\,/\,(A+C)\] ratios are always or almost equal to one.
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