Gene moving round in motor (6)
I believe the answer is:
engine
'motor' is the definition.
(engine is a kind of motor)
'gene moving round in' is the wordplay.
'moving' is an anagram indicator (letters are moved around).
'round' is an insertion indicator.
'gene' is an anagram of 'enge'.
'enge' going around 'in' is 'ENGINE'.
(Other definitions for engine that I've seen before include "Machine converting energy into motion" , "Motor" , "Mallard, perhaps" , "Machine supplying power" , "Machine doing work" .)