Medical procedure involved in gene mapping (5)
I believe the answer is:
enema
'medical procedure' is the definition.
(I know that enema is a type of medical procedure)
'involved in gene mapping' is the wordplay.
'involved in' says the answer is hidden in the clue.
'ENEMA' is hidden within 'gene mapping'.
(Other definitions for enema that I've seen before include "Liquid injection given as a laxative" , "Fluid injected rectally" , "Stern action from nurse perhaps" , "Medical liquid introduced anally" , "The bottom line in medical treatment?" .)