| Direction: Read the following and answer the questions from given below Erwin Chargaff was one of those men, making two discoveries that led James Watson and Francis Crick to the double helix structure of DNA. At first Chargaff noticed that DNA whether taken from a plant or animal-contained equal amounts of adenine and thymine and equal amounts of cytosine and guanine. These equalities provides clues into the chemical pairing that make up the double helix. In addition Chargaff also found that amounts of guanine, cytosine, adenine and thymine vary by species are indication that DNA, not protein might be the genetic material for life. |
| (ii) Which one of the following ratio is constant in DNA of different species? |
A) A+T/C+G
B) A+G/T+C
C) A+C/U+G
D) A+U/C+G
Correct Answer: A
Solution :
[a] According to Chargaff rule, in DNA there is always equality in quantity between the bases A and T and between the bases G and C (A is adenine, T is thymine, G is guanine and C is cytosine). So , A + T : C + G ratio is constant in DNA of different species
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