Question

According to Chargaff's rules, which base relationship is constant across all species?

• A. (A = C)
• B. (A = G)
• C. (A = T)
• D. (G = T)

Hint:

{Chargaff Rule:}
(A = T) and (G = C).
Purines equal pyrimidines in double-stranded DNA.

Answer 1

The Correct Option is C

Topic: Molecular Genetics (DNA Structure)
Erwin Chargaff discovered that DNA composition follows specific rules regarding the ratio of nitrogenous bases, which later helped Watson and Crick build the double helix model.
Steps:
Understanding the Question: Which pair of DNA bases always exists in a 1:1 ratio because they pair with each other?
Key Formulas and Approach: Chargaff's Rule states that in double-stranded DNA, the amount of Purines = the amount of Pyrimidines. Specifically, $[A] = [T]$ and $[G] = [C]$.
Detailed Solution:
Adenine (A) always hydrogen bonds with Thymine (T).
Guanine (G) always hydrogen bonds with Cytosine (C).
Therefore, in any double-stranded DNA molecule, the total number of A's must equal the total number of T's ($A=T$), and the number of G's must equal the number of C's ($G=C$).