Transform dog biting a European (6)
I believe the answer is:
mutate
'transform' is the definition.
(thesaurus)
'dog biting a european' is the wordplay.
'dog' becomes 'mutt' (mutt is a kind of dog**).
'biting' is an insertion indicator (I've seen this in other clues).
'european' becomes 'e' (abbreviation e.g. EU).
'mutt' placed around 'a' is 'mutat'.
'mutat'+'e'='MUTATE'
(Other definitions for mutate that I've seen before include "effect major change" , "Undergo change to another form" , "Gradually change form" , "Change in basic nature" , "Undergo genetic change" .)