What are common mistakes students make with chargaff's rule?
Chargaff's rule states that the nitrogen bases adenine and thymine occur in equal concentrations within DNA, and the the nitrogen bases guanine and cytosine also occur in equal concentrations. From this rule we get the base-pairing rule, which states that in DNA, adenine always pairs with thymine, and guanine always pairs with cytosine. This pattern of base-pairing is essential in insuring that the DNA will be replicated without error before a cell undergoes mitotic cell division.
The most common mistake that students make is not remembering which bases pair with each other. There are four bases: A, T, G, C. To help my students remember the proper pairing, I would point out that A and T paired together as they should be spells "at". This leaves the other base pair to be G:C.