He takes after his father presumably (4)
I believe the answer is:
heir
'his father presumably' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'he takes after' is the wordplay.
'takes' becomes 'ir' (I can't explain this - if you can you should give a lot more credence to this answer).
'after' is a charade indicator (letters next to each other).
'he'+'ir'='HEIR'
Can you help me to learn more?
(Other definitions for heir that I've seen before include "One set to inherit" , "one's to inherit throne!" , "Treasured family possession" , "Successor to position or estate" , "Successor, next in line" .)