Gets nice flies in branch of biology (8)
I believe the answer is:
genetics
'branch of biology' is the definition.
(I've seen this before)
'gets nice flies' is the wordplay.
'flies' is an anagram indicator.
'gets'+'nice'='getsnice'
'getsnice' with letters rearranged gives 'GENETICS'.
'in' acts as a link.
(Other definitions for genetics that I've seen before include "Science of heredity" , "Study of inherited characteristics" , "Branch of biology" , "The study of biological heredity" , "The scientific study of heredity" .)