I was reading this Wikipedia article on Mutational Signatures and I came across this section titled Types of mutations: base substitutions. I don't understand why the C>A mutations are indistinguishable from G>T. When we are cataloging the mutations we do have the strand information, right? Can someone please elaborate?
There are six classes of base substitution: C>A, C>G, C>T, T>A, T>C, T>G. The G>T substitution is considered equivalent to the C>A substitution because it is not possible to differentiate on which DNA strand (forward or reverse) the substitution initially occurred. Both the C>A and G>T substitutions are therefore counted as part of the "C>A" class. For the same reason the G>C, G>A, A>T, A>G and A>C mutations are counted as part of the "C>G", "C>T", "T>A", "T>C" and "T>G" classes respectively.