what is a change in the usual order of a gene's A, C, T, and G building blocks called?thx

Some mutagenic agents mimic nitrogenous bases and insert
themselves into the DNA. This is called a base analog. This changes the normal order in
the DNA. If bromouracil, a mutagenic agent, is inserted into the DNA, it acts like a
thymine and will pair with an adenine. This will cause a new base pair to be inserted
into the DNA. This will then cause a change in the original DNA. Another type of
mutation is the frameshift mutation. If a base is inserted or deleted either by chance
or due to DNA repair mechanism malfunction in the cell or due to exposure to mutagenic
chemicals, this causes a frameshift mutation. The DNA code is translated by RNA into
amino acids. Every three bases is a codon or triplet. If one single additional base is
added, or deleted, the triplets will shift and will not be translated into the correct
amino acid sequence of the protein. This will produce a longer or shorter than normal
protein, and possibly one that is not functional.