Dog that is following Antarctic explorer (7)
I believe the answer is:
scottie
'dog' is the definition.
(I know that Scottie is a type of dog)
'that is following antarctic explorer' is the wordplay.
'that is' becomes 'ie' (short for Latin 'id est', 'that is').
'following' means one lot of letters go next to another.
'antarctic explorer' becomes 'scott' (Robert Falcon Scott, Scott of the Antarctic).
'ie' after 'scott' is 'SCOTTIE'.
(Other definitions for scottie that I've seen before include "Dog" , "Type of terrier" , "Breed of terrier" , "animal" .)