To determine the correct base pairing in DNA according to Chargaff's rule, we need to understand the fundamental principles of how bases pair in DNA.
Chargaff's Rule states that in DNA:
- The amount of adenine (A) is equal to the amount of thymine (T).
- The amount of cytosine (C) is equal to the amount of guanine (G).
Let's evaluate each of the given options based on this rule:
1. Option 1: [tex]$A = T ; C = G$[/tex]
- This option states that adenine pairs with thymine, and cytosine pairs with guanine.
- This correctly follows Chargaff's rule.
2. Option 2: [tex]$A = C ; T = G$[/tex]
- This option states that adenine pairs with cytosine, and thymine pairs with guanine.
- This does not follow Chargaff’s rule, as it mismatches the pairs.
3. Option 3: [tex]$A = G ; T = U$[/tex]
- This option states that adenine pairs with guanine, and thymine pairs with uracil.
- This also does not follow Chargaff’s rule, and uracil (U) is found in RNA, not in DNA.
4. Option 4: [tex]$A = U ; C = G$[/tex]
- This option states that adenine pairs with uracil, and cytosine pairs with guanine.
- Again, this does not follow Chargaff’s rule, and uracil is applicable to RNA rather than DNA.
Conclusion:
Chargaff's rule accurately applies to DNA where adenine (A) pairs with thymine (T) and cytosine (C) pairs with guanine (G). Based on this knowledge, the correct answer is
[tex]\[
\boxed{A = T ; C = G}
\][/tex]
Therefore, the correct option is Option 1.
