How can we say that a change in genes can bring about a change in $DNA$?

(N/A) gene is a specific segment of $DNA$ located on a chromosome that codes for a particular protein or functional $RNA$.
Since genes are the functional units of inheritance composed of $DNA$ sequences,any alteration in the nucleotide sequence of a gene (mutation) directly modifies the structure of the $DNA$ molecule.
Because the $DNA$ molecule is essentially a long chain of these gene segments and non-coding regions,a change in the genetic code of a gene segment constitutes a change in the $DNA$ itself.
Therefore,it is accurate to state that a change in genes brings about a change in $DNA$.