______________ (11) is a change in the base sequence of DNA. It may affect only one _____ (12), or they may affect whole ______________ (13). It can also lead to changes in the structure of an encoded _________ (14) or to a decrease or complete loss in its expression. Because a change in the _______ (15) sequence affects all copies of the encoded protein, mutations can be particularly damaging to a cell or organism. ​