The order of the bases, A, T, G, and C, contained information. Because A is always paired with T and G with C,
the order of bases on one strand determines the order on the other strand.
Thus, if a DNA molecule were
unwound, each strand could be copied into a complementary strand, producing an exact replica of the original molecule.
Errors in the copying mechanism could result in mutations, or changes in the DNA sequence,
that could be inherited by future generations.