Insect from another world found by DNA expert (7)
I believe the answer is:
cricket
'insect' is the definition.
(cricket is a kind of insect)
'from another world found by dna expert' is the wordplay.
'from another world' becomes 'et' (extraterrestrial).
'found by' means one lot of letters go next to another.
'dna expert' becomes 'crick' (Francis Crick).
'et' put after 'crick' is 'CRICKET'.
(Other definitions for cricket that I've seen before include "short leg seen on this field?" , "Insect with long leg" , "a jumper" , "Summer sport" , "English game or chirping insect" .)