D. DNA Base Composition (the Magic)

Question 1: For a double-strand DNA, if I tell you that the base content [A] = 20%, what is the base content [T]? How about [G] and [C]?

> Are you kidding? This is what we were told at Genetics class. And the answer is [T]=20%, [G]=30%, and [C]=30%.

Question 2: If I unzip the DNA double helix and throw one strand away, I now have a single strand in my hand. For this single strand , if I tell you that the base content [A] = 20%, what is the base content [T]? How about [G] and [C]?

> I can not tell.

Well, [T] is about 20%, [G] is about 30%, and [C] is about 30%. Most of us do not have to worry about all this. But it is fascinating once you look into related questions. In evolution, what are the base compositions of the first DNA molecular?

Evolutionary Patterns of DNA Base Composition and Correlation to Polymorphisms in DNA Repair Systems Nucleic Acids Research 43:3614-3625.